(...) Chuck made it clear that the former resident wasn't going to return. (...)
That doesn't mean much because it's Chuck's house so even if Darius would return Chuck wouldn't let him stay there. Either way he's either dead or a guinea pig for Abel who for all we know might even have (Darius') keys for the apartment.
(...) Maybe Chuck is Mr. Nice Guy in general and helped Victoria financially since she ended up quitting her porn career? (...)
He's definitely not, at least not to whores. Victoria made it rather clear that she's not too content about Edwin's reconnection with Chuck but not explicit enough for Edwin to know what's really behind her words.
(...)
And what about Grace's line about “the messages Chuck left for people who insulted him”? What if the reason Chuck was teaching a class at the school wasn't because of Ian, but because of this "message" thing intended for Victoria? (...)
That line bothered me too and your theory makes total sense, although I don't think it's the case. While Chuck is a total pervert his main passion has always been science (he admitted to both, i.e. that he's a total pervert and that physics is his real passion). I wouldn't be surprised if after meeting Victoria (who has
humongous breasts) being the pervert that he is he would talk about her to August and Donny saying how awesome it would be if she would star in a movie and Donny would say
"but she did star" :].
Either way, Chuck could mess with Victoria and put pressure on her in a thousand different ways, there would be no reason for him to teach Edwin for that. And his affection towards him seems genuine, plus as you've said, him saying to Kat to not mess with Edwin as far as porn acting is concerned suggests that he doesn't want Victoria to get hurt (if only because that would hurt Edwin).