sweet, hadn't thought about places. let's see...
I kinda doubt Hanako would want to have sex anywhere someone could see her, though I do have this great mental image of them kissing in the tea room and they haven't told Lilly that they're dating and Lilly comes in when they're lip-locked, so they have to sneak out very, very quietly.

and then, of course, they'd run into Rin in the hallway right outside, and she'd announce their presence.
and yeah, I think sex with Rin in the art room will probably happen. just 'cause. the real question, is she going to want Hisao to pour paint all over her and himself and then they make sweet art on a giant canvas. maybe a little out there, but at least they definitely wouldn't say if it was good or not until they were done. probably.
as for Shizune in the student council room, depends on if she likes mixing business with pleasure.

dunno how adventurous she is, it's not the same thing as being competitive, so it's kinda hard to say. I can say that I'd be totally in favor of going at it in Misha's room when Misha's not there, just in case Misha shows up.
Lilly also doesn't seem that adventurous, but it's really hard to say just from act 1. I really don't know where she'd want to have sex (besides, y'know, the bedroom).
roof's a good one for Emi (and Rin, now that I think about it), also maybe some place where they keep the PE equipment and stuff. or some shelter near the track, if she and Hisao are out there and it starts raining. of all the girls, I think she'd be the most likely one to be spontaneous about it, so she's most likely to end up with a sex scene somewhere unusual.