Alright, summarizing my thoughts about ST...
*Obedience is a must have, we cannot use disposition alone for everything. It should be the same stat for everyone, but it could be called obedience for slaves and, for example, dedication, allegiance or loyality for free ones.
*Sensitivity from both Valet and SM. In the first game it means both physical and psychological sensitivity, in the second one it means physical only. Depends on how deep you want to simulate girls psychology. Basically, using too rough punishments and too perverted training/actions descrease it in both games, and vice versa.
*Escort, singing/dancing/music, healing, clerical work skills we could add at some point, providing that there will be jobs using them, not necessarily within brothels. Right now we don't have such jobs, we most likely will at least some of them in the future.
* BDSM skill is a must have.
*I'm not so sure about group though, basically you do the same thing, but with many people, so... Maybe we should use stat like pride/libido/obedience or something like that, so if pride is high enough for example, then a girl will refuse to do group.
*Petting. Both Valet and SM have it. Maybe we should too. In Valet it's a prelude to sex, in SM it's masturbation types of skills, basically.
*We could port a lot from Valet, I doubt it will ever have translations.