MIDlands Charater Creation

Neal,
With regards to chance of improving one's skill, I use the RuneQuest rule: You can try to improve the skill, only if you used it in the course of the adventure to achieve the positive difference and move the story forward. All the skills that were used (and that includes spells) become candidates for improvement. For a healing skill, it is not enough to cast the Cure Light Wounds Spell, you must have cast it on enough players to make a difference between players losing the melee and winning it. Healing skill has to be used to stabilize a character with zero and less HP and to keep him or her from dying. Magic Missile spell would be the candidate for improvement if it drops (or kills) an opponent. The frequency is ONCE per ADVENTURE. You can use the skill successfully to move the adventurers forward a dozen times, still, it only gets ONE shot. Another thing to consider, is how long an adventure takes place. For instance, My players just came off a two year long mega dungeon adventure that lasted from beginning of May until end of July in game time. I have a Magic User, who used a Sleep spell successfully at least a dozen times. Since the skill improvement represents a lifetime track record, that player will only get 1 chance at improving that skill. To make sure that he gets the improvement, I might reward him with an automatic maximum success, OR I can add the number he used the spell to attain critical success to his percentile die roll to see if his skill improves. Another thing to consider is that since Sleep is a first level spell, which the player has mastered. If he practiced the spell with another wizard, who has sleep spell and is of significantly higher level than the 1st level, it only takes one week's supervised practice, before the skill improvement check can be made. When assessing amount of time it takes for training, you should decide as DM how long a training period should take. To learn to walk on one's hands the player character mist have high STR and DEX of 16 and will take 3 to five training sessions. To become an acrobat might take 2 -3 years of active study. Healers and Herbalists may gain experience by working as healers. A season (winter, summer, give or take spring and fall), might be long enough to warrant a skill improvement check, OR a critical incident that is role played successfully that might last one evening. Have the player character treat a patient dying from human rabies. If they got enough wherewithal to make a positive difference, they get to roll for skill improvement. Again, this is rooted in narrativism, and is largely at DM's discretion.
So, you want to play a wealthy Princeling, why not? Write the DM a brief backstory that I will modify accordingly. Placement-wise, you are from the large MIDlands city-state of Starohrad, five days by the river away from the local produce walled town of Ryeland, that is the base city (well... a large town) for the players. I would let you be the Princeling from Ryeland, but the place is so small, quiet and backward, that it doesn't produce enough wealth to make a Princeling! MIDlands narrativism is where story balance is maintained. I make a social class roll for each player character to see how bad the DM's rewriting of your story will be. If you want to be from the top 1% of the MIDlands society, you will probably have to roll 99-00 on percentile dice to enter the game as a fully empowered princeling that you are anticipating. But let us say that you rolled something other, that brings you more to the ground level of peasants or artisans and craftsmen or freeman homesteaders. That would mean that you are a Princeling-in-exile, and a DM has to make up as to what happened. For instance, "Your mother cheated on your Leonian Nobleman father and he had her burned at the stake as a witch. The Rogue whom she cheated with was hunted down on the forest and you lovely Dad has severely beaten his man at arms, who accidentally killed him while taking him alive. You were in the way of your step mother and their new baby and they sent you to a Monastery for schooling. You thought that the priests were going to kill you and you ran away from them... (eventually becoming a thief that the player character had)... and that is how the backstory for each player character gets written, maybe less extreme than this case, but no less dramatic...
There are THREE ways the players can roll up a character to enter Midlands, and none of them let you lower some ability to increase the other, hence, no Min-Maxing! The Man On The Street; The Dilettante; and roll to get a particular character class, everybody gets to be any AD&D character class they like, remember. Man On The Street rolls 3d6 for each ability. The good news is that you get to reroll as many times as you like, until you get the stats that you crave! Because 3d6 versus ability gives you least advantages, and restricts your choice of the character class, this represents the typical upbringing without any special attention paid to the child. Because of this, the character relies more on his friends and neighbors to get along in the world. What this means is that the Man on the Street is written into the setting more, with more contacts, more recognition based on CHA and a few more background/cultural skills.
The Dilettante rolls 4d6 for each ability, and you can re-roll as many times as you like until you get the stats that you crave! In the real world, the dilettante is a dabbler, who is not involved in the field as a professional, but practices it as a hobby. This was typically, because their families had enough money, to where they did not have to earn a living and could become a dabbler. A sailor goes to sea to support his family. A dilettante goes on a sea expedition  as a self-styled naturalist, journalist, or an adventurer. By the same token, rolling 4d6 and picking 3 highest, gives you more opportunities and represents more attention paid by parents, better grub fed to the child, and better social position. That does not necessarily mean wealthier, for there are poor families that are loving and are well integrated into their community. Because the Dilettantes typically have the luxury of privacy and solitude, they get no advantages of the common men on the street. 
Finally, if the player wants to play a particular character class, they can re-roll the lacking primary requisite attributes on a special table, that while reflecting the probabilities from the 3d6 bell curve, will yield only the numbers that will qualify the player for that character class. Bards, Monks, Paladins etc. Of course there is a trade-off, and that is where the MIDlands Narrativism comes in. Unlike other games I played in, the true Sandbox exerts Lovecraftian tentacles over the players. Each character is WRITTEN into the setting via the background essay like Silva's Tale. The player character is bound into the setting by a number of acquaintances and relationship with those acquaintances. Typically, a player gets to pick a number of "friends" in the setting equal to their CHA bonus. Equally important to the campaign development is the concept of the CANON. Player and a DM create the character's biography that places the character in the sandbox. Whatever elements of the story are agreed on, become part of the canon. If the bio thingie says that you are friends with Merlin or Conan or the King, then later in the game, if you ever get in touch with these NPC's, they will act as a benefactor on your side. How much can you get out of a friendship with a King? This is where the game ceases to be linear/by the rules and expectations, and enters the non-linear narrativist turf.
The trade-off that players exchange for the amazing choices available at the start of the game is in their independence of their characters. Most fantasy role playing games are run and played by middle class suburbanites with the expectations of the relatively privileged suburbanized white males. Almost everyone takes privacy/solitude for granted. This applies to the players sense of themselves in the real world as well as that of their characters. Essentially, a typical character exists apart from the game world, typically existing in the player's imagination as a self-sufficient traveler, who advances in their chosen profession (character class) by virtue of "experience" - loot and combat kills, which have little or nothing to do with the advancement in their chosen occupation. Typical D&D adventure starts with the players arriving into a town, getting a room at the inn, that mirrors their own room in their parents' home somewhere in the suburban sprawl. Next thing they do, is go to some "tavern" where they pick up rumors about some dungeon waiting to get looted. This is the purview of the Dungeon Master's world. Somehow the locals are totally ignorant of the riches in their midst, just waiting to be taken from the hordes of the sub-human two legged creatures ripe for slaughter. If it wasn't for the Orcs and the piles of gold pieces, I would have thought that the players were some mining company employees looking to extract the wealth of some God-forsaken 4th world nation like D&D player characters taking gold from the dungeon. Of course, one of the casualties in this adventure, is the players own vision. Typical D&D play proceeds like lovemaking in the seventies after the Joy of Sex came out: During the act of copulating, everyone is working to get themselves off, while going through the motions. The player can and will, come up with a backstory for their character, usually lovingly crafted and cherished one, and it has no more chance of surviving in the dungeon adventure than those new arrivals to the Nazi death camps selected to go take a shower or the inhalation lung treatment. The only thing that matters to the DM is the player character is expressed in terms of the game statistic that make the character playable in the context of the immediate adventure. In the final analysis the independence of the player characters is illusionary, since the only thing that counts is the in-game stats, which give the player a seat on the DM's rollercoaster.
To counteract this, The player character is written into the MIDlands setting at the start of the game. The freest ones are the Dilettantes, since they get to start the game on their own terms, a few negotiated close friends and a few problems, disadvantages, issues, by agreement with the DM. The Man on the street has more immediate resources and creature comforts, but they are part of the local story and they are least likely to enjoy the scenario of the merry traveler from far away. Those who choose to play a particular character class have the least freedom. They are considered to be in the active service of whatever organization or order employs them. Rangers, Paladins, Monks, Bards, are essentially institutionalized or closely affiliated with secret and secretive orders and organizations. They don't have to worry about level advancement or getting or finding instructors, but the DM can send them on an adventure (via NPC's who are their bosses), and they can't say no without reverting to regular fighters common men etc. By comparison, MIDlands thieves and magic users can act as free agents and have to role play finding guild affiliation and it is usually quite hard to find regular employment with the entities that train them. Even fighters have to travel the fantasy world looking for fencing instructors, but they have easier time joining military organizations and can move in and out of them, if they like.
Vagaries of embedding the players in the game world aside, there is one other important dynamic. Every set of stats that was rolled and discarded by the player as unsuitable, is not thrown out, but is taken by the DM and is used to make the NPC's who will be that player's Nemesis and will go after the player character and try to kill him or her throughout the course of the campaign.
End notes:
With regards to the spell-casters wearing fighters helms into battle. Assuming that a starting chance for the 1st level wizard casting a first level spell successfully acquired is in the ideal range of 25-40 percent; Spell-caster can wear an arming cap or an open face helm with no penalty; a 3/4 helm with a 15% penalty; and a helm with a visor that can be opened and closed with a 20% penalty.
I will go over the three books in separate posts.