It was less the perving on dead girls than the perving on corpses, I think, that bothered Tatsumi? ^.^

I think the souls of the dead live in Meifu until they reincarnate - I'm presuming Tsuzuki's landlord and his wife are in this situation.

There are also stuffed animals left on Tsuzuki's bed at the beginning of book 5 with a label saying Kazusa left them. I'd take that to mean she was still in Meifu and visited Tsuzuki, given the length of time elapsed between Devil's Trill and Bookverse (and the fact that she seemed to stay at the main building all through Devil's Trill).