Where does Vincent live (post-game)?
I've never been fond of the pervasive fanon that has him move back into the Shinra Mansion - apart from being infested with Dorky Faces and other critters, that place is the site of his worst memories. (Not to mention that DoC has jossed this particular fanon anyhow, since the part where Vincent goes to Shinra Manor contains no indication of him normally living there.)
Of course, that leaves the question, "Where does he live?" Even assuming he had his own house/apartment before his thirty-year nap - well, he'd have a hard time proving it's his. (Can you imagine it? "Hi, I'm Vincent Valentine. This is my house; and I wanna move back in, so kindly move out!" "You mean, the Vincent Valentine who's been 'missing, presumed dead' for thirty years and would be thirty years older than you even if he wasn't dead? Riiiight.")
So from that POV, I can see where the "he moved back into the Shinra Mansion" fanon is coming from - it's an empty house (well, empty aside from the monsters) that no one's laying claim to, so if he was in need of a roof over the head...
I'm sure Cloud and Tifa would let him shack up in a backroom of the new Seventh Heaven if need be, but the "Vincent left just like one of those passengers that would sit next to you on a train" line in Case of Tifa implies that he didn't take them up on the offer, if such an offer was made.
Likewise, I'm sure he'd be welcome at Cid's and Shera's house, but I also think he wouldn't want to impose, especially given that there isn't much space (have you ever noticed that Cid's Rocket Town house doesn't even have a proper bedroom?).
It's possible that he stayed in Kalm for a while - Case of Tifa also contains a reference to the residents of Kalm taking in refugees for free. But we know he no longer lived in Kalm by the time of DoC, because in Reeve's text message at the beginning, it says that he (Reeve) arranged for him to stay at the inn. If Vincent had been living in Kalm at that point, he would've stayed at home rather than at the inn, right?
Hey, for all we know, he may have lived in Cosmo Canyon for a while, letting the atmosphere soothe his soul and spending time with Nanaki. (Or maybe I just say that because I love Cosmo Canyon.)
I also think it possible that for a while, he lived in the Forgotten Capital at least part time. (Didn't he say something along the lines of "I come here often" in AC?) Those conch houses look comfortable enough; and it would have allowed Vincent to have solitude (it's the Forgotten Capital) while still being able to contact civilisation (due to Bone Village being close by).
Or maybe he's really been itinerant for the two years between the game and AC, passing through like a passenger...
How does Vincent sleep?
As in, what are his favourite sleeping arrangements? Does he sleep in the buff (heh, us fangirls can wish...), in pajamas, in his clothes? One idea I've seen in fanfic is that he sleeps naked because sleeping clothed reminds him too much of his time in the coffin. Myself, I've always imagined him sleeping clothed, though, both for psychological reasons on his part and for practical reasons - with that claw hand and the many buckles on his clothes, (un-)dressing himself has to be quite the chore, so it's easier to just keep his clothes on. (But then, he has to take his clothes off sometimes to bathe, so... I don't know.)
I'm wondering if having been in that coffin in a locked basement for so long means that now he can only sleep with the door open and the lights on because he'd get claustrophobic otherwise? Or maybe it's the other way 'round, and he can only sleep in a closed, dark space because that's what he's become used to? On a related note, I've always wondered how well (or not) he slept at the Ghost Hotel, because the spooky ambiente must have reminded him of his basement room for sure. That is, if he could even take it seriously - "What's with these silly artificial bats? I've been locked in the basement with real bats and Yin-Yangs!"
Any other thoughts?