So I think that these characters should have the following bonuses:
Adventurers
Trappers: 10% Bonues in setting traps
Wanderers: 10% Bonus in stamina
Indians: 10% Bonus in animal instincts
Prospector: 10% Bonus in trading
Duelers
Bounty Hunter: 10% Bonus in shooting
Gunslinger: 10% Bonus in aim
Bandit: 10% Bonus in dodging
Hangdog: 10% Bonus in appearance
Builders
Cowboy: 10% in tactics
Quaker: 10% Bonus in repairing
Craftsman: 10% Bonus in constructiong
Mortician: 10% Bonus in fine motor skills
Soldiers
Cavalryman: 10% Bonus in horse back riding
Mexican: 10% Bonus in vigour
Mercenary: 10% Bonus in toughness
Iroquois: 10% Bonus in reflex
These bonus will help players to focus more. For example, if an adventurer would like to be a Trader typ, he would choose Prospector. If he wants to be a Trapper typ, he would choose the sub-character class Trapper.
And I also think that after reaching a certain level, the character class should be upgraded. I propose level 30, level 60 and level 100 ad so on, so every time the character class upgrades, it gets an additional 10 level harder to reach the next upgrade. With every upgrade, the character bonuses increase by 3-10% (so just a slight increase, maybe the higher the title, the more will be increased) and the player receives a new character class titel. Like adventurers could be scout, woodsman, tracker, and trailblazer. Duellers could be young gun, gunslinger, quickdraw, and sharpshot.
And both mastering the first/previous character quest and reaching the next upgrade/title will be prerequisites for doing new character quests (, which need to be introduced in the future).
Will still can discuss about these details (names, precise bonus rates...), but I think it's a good concept.