There are 4 main girls, Jane, Anna, Lisa and Selina. In those there are maybe a couple of 3some's that will happen like Lisa and Jade. The other possible one is Anna and the red head boss.
As for other side girls they aren't real paths and probably won't lead anywhere.
in the script there are the variables: lisa_path, jade_path, rosa_path, selina_path. that tells those are currently the 4 female characters with a route already established. it's interesting that during the 3some scene with Lisa and Jade in the last version the script only checks for the jade_path variable and not lisa_path.
Jane has instead the variable jane_date_offer that most likely will bring to a jane_path variable in one of the next updates.
Anna only has the anna_sex variable associated to her, that isn't enough to tell right now if Anna will eventually become a love interest or stay as a sex on the side thing. same for Emma that currently has only the day09_emma_lewd variable.
a 3some with Anna and her boss could be a thing, but Cath in the last update has crossed into Rosa's storyline as well, so that might become a thing too.
Rosa is only possible by going on Selina's path or you won't meet her. It should be possible to break things off with Selina when she brings up her story but I haven't tried it so not sure if Rosa's path continues if you break up with her daughter. In theory it should.
Rosa's path continues even after breaking with Selina, it just takes away some dialogue options and branching choices, you will be just forced to take the Rosa's path options.
I already did it, none of my previous saves worked....
some saves from v0.45 won't work cause the dev has modified most of the Jane's path and some of the Rosa's path from the last update adding content to it, so Ren'py will not find a place to roll back when you load the save. check if you still have saves before the part in v0.45 where the 1st visit to Rosa happens, those saves should work.
