Ayua (the asian girl) wouldn't make much sense if you are in Bella's route specifically, I don't think she would cross Bella as she seems to really like her and is happy for MC and her getting closer, also she knows how Bella is. I just can't think of who would get their first scenes, I know who I want to, but there is so much to be seen yet.
Nia could get hers first, but at the same time it would be strange, lewds for her would be a no brainer, unless she wants to show MC that she is more than just a cam girl, which I feel is what Ocean is going to do and I'd like that approach.
And one last thing, if we use the CG gallery to determine who the main girls are we have Bella, Milla, Nami, Nia and Sasha for now, but I get the feeling that those aren't all, Sonya being the banner for the game most likely is a main girl, Victoria has a lot of screen time to not be a main girl and so does Maja.