Yes and no. Yes, those seven listed are the seven official love interests (LIs) of the game. Other girls are side girls, who do not have an official path. You do have the option, therefore, of having seven separate paths, one for each. You can currently, however, have all the girls on a single save, depending on choices made. You may miss the odd scene here and there if you are on a path where you would be required to be in two places at once, but I don't think there are many of these, if any at all (I've not really looked into it, but I don't think there's much, based on the gallery).
Harem is being worked on, and indications from the last update are that it is now going forwards. If that is actually the case, of course, remains to be seen.
As far as paths go, outside of the girls themselves, there are certain key points that open up different avenues. The main example I can think of is when a side girl offers help, and depending on previous choices made, you might have two or three options here as to what she helps you with. At least two of those can have a positive effect on your relationship with the appropriate LI.
Sidenote: Roxy is my favourite in the game, but like you, I missed most of her content in my first playthrough because I made a couple of "wrong" choices.