I have recently found this game and have been enjoying it.
My suggestions:
Setting up separate XP scales in options for both PC and slaves so that you can change how much experience is needed to level up. Thus for those who just want to rush through the story, they can set the experience to basically level every time they go into combat, and for those who want leveling to mean something, set the experience much higher so that it becomes a rare occurrence to actually level up. This coupled with the slaves dying in combat would make for a real challenge in the game.
Having the game set up a 3rd folder for body images for the intimacy/rape scenes. Just as some of the named NPCs have different body pictures whether you are viewing them in the mansion or in the bedroom, a way to do the same with normal slaves. And regarding the auto select portrait method, if there was no matching picture in the intimacy folder, to just fall back on the regular body picture.
An game option for when slaves work in a town where you are not situated (for example Slave Catcher in Gorn while your mansion is in Wimborn) the slaves have to pay the fee to use the portal back to the mansion. This will provide an incentive to level the slaves until they are experienced enough (story wise) to provide a profit in the distant jobs away from immediate supervision.