Talking to someone in the dungeon covers plenty of this.
I think it's too easy to collect new slaves when you go into the endgame rather than too difficult. You can collect as many high end slaves as you have rope, essentially. There doesn't need to be an extra pool of people to collect.
I think people would like more drops from creatures and something to do with those drops if someone can make a full system. Personally I'd rather make fights with wolves more interesting (by improving the fight mechanics) before adding extra reasons for people to fight them. I don't like the alchemist start as that it encourages you to do the dullest fights (monsters) instead of something interesting (slaving).