I take those scenes as they not feeling ready to take that step but still wanting to do something
I think you're looking more at motivation, and I'm looking more at how they did it. Yeah, everyone wants MC--again not very realistic, but goes with the genre. We know Nova was attracted to him immediately (she was checking out the picture of MC in his underwear really carefully), but yeah, she was pretty much forced into the BJ, even though she later admits to herself that it was "kinda hot." I don't recall such direct evidence of Dalia's attraction to him (other than teasing about her lack of a gag reflex), but (1) she was willing to bet a BJ, and (2) allowed herself to be argued into it with a pretty thin argument. Luna, by the time we got to it, she just wanted to do it--she said as much, that she'd wanted to do (and would have done) it earlier if they hadn't been interrupted. So I agree with you that the motivation in each of these cases was realistic enough (granting the "everyone wants MC").
My point is that, once the BJ is happening, none of them look like it's their first (or even second, or third) BJ--and frankly, we probably don't want to see an average "first BJ."
Same with Rushed Break--sure, at some point, most virgins have sex and stop being virgins, and MC and Nova were plenty into each other (even if MC needed Nancy to literally knock some sense into him). But they don't do it like that. And again, we probably don't really want to see two virgins having sex for the first time, because it's likely to be fumbling, awkward, and not especially sexy.
So while yes, the motivation for the sex acts is generally realistic, the sex acts themselves generally aren't. I guess the "threesome for Nova" question kind of straddles this fence.
This isn't a criticism, because the whole game is a fantasy. Especially the part about being surrounded by beautiful women who just can't wait to get into your pants (they may or may not be or fall in love with you (which I'd prefer), but they definitely want you). The wild, athletic, acrobatic sex is just another aspect of it.
I don´t know if Alex or Penny were virgins
It isn't stated as of the end of 0.7 (again, I haven't seen most of 0.8 yet), but I've heard some pretty passionate argument that there's no way a virgin would engage in Christened Apartment. But if that argument's valid, then there's no way Nova was a virgin either going into Rushed Break--and we know she was.
I'm now leaning toward Alex not having been a virgin based on this:
...and what followed. It's not conclusive, of course, but (assuming she isn't just talking out her ass) it suggests similar past experience--where she's deliberately trying (and succeeding) to tease men, to at least make them nervous. That, of course, wouldn't mean she'd had sex with them, but I think it points in that direction.
Penny, I don't know one way or the other. Beautiful and popular (and nice, so therefore likely approachable), she surely would have had plenty of offers, but no serious boyfriends, and doesn't seem like she'd be up for just a hookup. So I think my guess would be "virgin," but not with any conviction.