So I had put this aside, but started thinking about this again. I think I have some rules that make sense.
First off, all characters begin in a fashion like normal men, with 4 general proficiencies. They may also get bonus proficiencies for high intelligence. Use the starting age rules, and allow characters to advance the age of characters in exchange for additional general proficiencies. This will likely result in age related penalties to ability scores, so monitor this closely.
At levels 1 to 4, characters get class proficiencies as normal, but no general proficiencies. Instead, at each level, they select an “adventurer” proficiency. These are:
Equipment care: You know how to maintain your equipment independently, especially arms and armor. You may also supervise the equipment and armor of 3+int bonus others. Characters whose equipment is not being taken care of move as if their equipment was one stone heavier than normal. Arms and armor will deteriorate each day they are used in combat but not maintained. For weapons, record the max damage done each day, X. At the end of the day, roll 1dX on the scavenged weapons table to determine the deerie ration to the weapon. Similarly, record max damage done to a character in one blow during the day, Y. Roll 1dY on scavenged armor table at the end of each day. Having to maintain others equipment
Dungeoncraft: You are savvy in underground environments, and are familiar with dungeon exploration procedures. Characters with this proficiency can read maps, and can create maps with if traveling no faster than their exploration speed.
Characters who lack this proficiency suffer a -4 penalty to rolls to hear noise, locate secret doors, or force them open. In addition they have a -1 penalty to surprise rolls underground.
Bushcraft: You are savvy in wilderness environments. You know how to ride and saddle a trained horse under normal conditions, how to camp and prepare food in the wilderness, and the basics of how to find or hunt for food. You can also manage the camp details of 3 + int bonus others.
Characters who lack this proficiency suffer -4 penalties to foraging, hunting and navigation rolls. They also use one additional days rations and require one additional days rest per week of wilderness travel.
Moneycraft: You know how to handle money, what it can buy, and what it can be used for. In addition, you can determine the basic value of treasures and trade goods.
Characters without this proficiency suffer a 10% penalty in prices when buying or selling, as if their opponent had the bargaining proficiency. Those without the proficiency may attempt to evaluate treasures on a roll of 11+. Each point by which the roll is failed results in a 10% valuation error in a random direction.