service sororitys

since these sororities are like you said not 'real' they get to make up their own rules. if you rush them you cant do formal recruitment which is up to you but then you're also limiting yourself to these 4 that tbh people dont take that seriously. they can get a pledge class roughly the size they want especially esa and trilogy cuz they're the most relevant and get the girls they want.

Ophia is technically under associate Panhellenic, so you'll be able to do Greek events like derby days and Greek week.
ESA is supposed to be coed, so I don't know how long they'll be able to have pledge classes of all girls.
Personally for me, the girls in trilogy that I know are really tight, fun, and for the cost, totally worth it if you just want to have fun.

In terms of pledge class size, it's all up to them. If you want to specifically rush one of theses, you could do it in the spring if you don't get a bid in the fall