Okay, so, this is a fascinating question that I've honestly never thought of before!
So, for Ellen, assuming we're past the Social Problems she has up until she starts getting more comfortable and setting down roots in the Korps, she's the sort that enjoys a tight selection of close friends--Vixie, obviously, plus Volta and Carmen, and maybe you can squeeze Wren and Mabel in there as things develop--but for most people she prefers a sort of loose acquaintanceship with the occasional pick-up. She doesn't have to know someone super well to play tennis with them a few times a month and both of them have a great time, for example, and to some extent she's content to interact with people she's going to lump into the category of "fans and admirers."
But obviously that's not an impenetrable difference and someone can start as an acquaintance and move their way up--Ellen's just not going to be the one to really drive that herself.
Vixie, meanwhile, tends to lump people in a middle zone: her approach to friendships (and sexual partners--she tends not to differentiate the two) is to have as many as she possibly has time for and bounce between them whenever she's wanted (and kind of just Show Up when she's free), so she has a lot of friends--but not a lot she's likely to hang out with multiple days in a row (as opposed to Ellen, who will happily spend a week+ with anyone in her close friends group). Her closest friends are a little further and her furthest friends are a little closer, basically, than Ellen's, and as such it's hard to put a number on them.
(That said, Vixie's closest friends are probably Ellen, Volta, and Roxie!)
