5. Drug food to increase arousal with each day
I like this concept, if you can give pigs in the barn cookies with hunger drugs to fatten them, it doesn't sound too crazy that you can also put mild aphrodisiacs in the slave's food, in theory, lorewise and mechanically makes sense, but in practice... it may be too op? while the philtre potion may be the strongest potion (the one that gives 1 free devotion) aphrodisiac and super aphrodisiac potions are still very strong too on their own, with a couple of those you can rank an F- slave to D- in the first week if you know how to play your cards, having an "aphrodisiac food" rule may be like having early aphrodisiacs which would be very strong, but it being too op may depend on 3 factors:
1.- how much it costs
2.- how much arousal it increases
and (another thing that makes this interesting)
3.- how harsh are the penalties for breaking "deny masturbation" and "deny orgasm" rules on the training
About the first it obviously needs to be expensive, making aphrodisiacs is expensive, it takes 3 different ingredients ($10 per batch) + alcohol ($5 per batch), that's without taking into account the cost of training the alchemist (spending on school for months, renting an apartment + lab, etc) and that's also without taking into account that those are the costs of you making the potions not the potions being sold to you by someone else to make a profit, so it has to be very expensive ($5-20 a day?)
About the second point, the effect has to be very low, kinda like the effect that clothes and piercings have, maybe those effects would have to re balanced because of it.
And the last one, those 2 rules can't be broken normally but this kind of rule would make them breakable earlier which I find interesting, would this kind of strat work in the early game? not sure, on one hand it could have a very high paywall and the effects may not be strong enough, on the other hand if by paying extra for one week means that you can sell your slave a week or 2 earlier it could become a tier 0 strat that would break the game as the sundress/soft slippers did some time ago.
Makes sense but I find it hard to justify given how much things cost in the game, $2 sounds like too much, $1 sounds like enough but that's still like 1 free gown per decade, what would you get in return? a mood boost is too much, besides the mini pony reward fills that daily cost role although it's more expensive
6. Rules could be expanded: undress while in home, always barefoot to toughen feet, undress when called unless not dressed
I guess a "stay naked" rule could be implemented and be some sort of "unbreakable" rule like deny orgasm and deny masturbation that forces her to take off her clothes, but it sounds very convoluted to implement, would that make her take off her collar? that comes with the risk of her fleeing, if the "stay naked" rule is on, would you be able to assign the outfit anyways and pretend she is naked until training comes? when it comes to training time will she put her outfit and take it off when she's done? otherwise why buy an outfit if she won't put it on?
masturbate self continually to stay aroused
Vaginal beads fill that role.
7. Influencing current interests could be... interesting. How she feels about something can always increase or decrease such as public nudity on the beach, fields, adventuring and so forth.
If I'm not wrong, slaves can win some traits depending on how much they do certain things, it's very slow but a slave can become an exhibitionist for instance if trained for enough time aiming at that trait.
8. I think it'd be good if there are non-cruel methods if the player cares for the slave. It may be slower, but the slave may recognize the player isn't evil and wants to help her with her interests, education, and others.
It may depend on what do you mean with "non-cruel method", technically you can train a slave without ever hitting her, by explaining her position you're trying to reason with her, by just using scolding as a punishment, by starving her and make her sleep on the floor, unless you consider those "cruel", it takes more time but it's possible.