1. Training a certain skill (not immediately but + to the maximum roll per level)
2. Temporary trait (strong, healthy, agile) with some chance of +1 to the target statistic after its removal.
3. Special trainig for veterans with permanent injuries in the possibility of some reduction of negative consequences.
I like these ideas.
If you could pay higher amounts of money to have recruits reach higher levels eventually, how would that differ (much) from just paying more money to recruit a sellsword who is already at level 4-5? Would it just be a somewhat cheaper but more delayed way of achieving the same thing for a background that never comes with ready experience? Not that I’d entirely dislike that, since it would make more backgrounds more useable later into the game …
However, I prefer the process of gradually building recruits up, one level at a time, via battles. I’d like it to be quicker, but I still want it to be step-by-step. It’s just a shame there aren’t more enemies later in the game that are suitable for “farming” experience for raw recruits …