Fear being reduced is a good thing, in my opinion. Don't be afraid to break their will utterly first so they obey even when disobedient, before you start building them back up, though. I've successfully taken a defiant slave to subservient without issue, myself- you just need to spend all your time with them and getting them willing to obey, mood-wise. Some might say it's more trouble than it's worth than breaking them and rebuilding them in the image you desire them to be, as there's no negative for doing so, but if you're roleplaying a benevolent (though strict) master, that's your choice. Personally I prefer to focus training on them one at a time anyways, because then you don't have to spend time breaking their will for the remainder of the week, unlike if you just dabble with a few. Big tip on that is to discipline or reward them a couple times as you see fit, then hit them with a sexual stimulus to get them to oversexed on the 3rd action; you get two more actions, which you can spend doing whatever, and their oversexed status will push them towards a better mood and much better compliance with your orders, rather than suffering the penalties of being oversexed for too long. The next time it's active you'll have them at horny, which will continually increase their mood and make it so that your training is much more effective; you'll quickly get them to ecstatic (200% rate) and so long as you keep them in a good sexual mood they'll obey much more easily, even without taking into account submission and will levels.
As for male sluts, I think you have to use the Alteration Potion line of elixirs to convert them from males to females physically, while they retain their male gender identity, and then train them in strumpetry, which unlocks when the potions are done their thing. I don't know if that actually qualifies or not, though. It could just be a code bug where it takes a title and a slave type and requests it, even if they aren't mutually compatible, but it'd be worth it to make a save just to test if that qualifies.
