Its been over a month now for me since my first (and only) interview and still not a peep from the school or my POI. I'm beginning to fear no news is bad news, and that they have extended offers to a few students, and they are waiting for the students to accept or decline the offer. However, like I said, I haven't been informed of being waitlisted either. Sorry for not answering your questions, haha, I'm new to this too and unsure what to expect.
After the interview weekend, in fact probably the day following the interview, I'm fairly certain each professor had to have an idea of which student s/he wanted to accept. I'm sure most schools form an admissions committee and have to approve as a group which students to offer admission. The only thing I can think of to delay informing students of their status (over a month, assuming they haven't notified any) is determining the amount of financial aid they can offer each student, which for the program I applied to isn't set in stone like other PhD programs.