I'll stick with Nate and Allen, I'm still finding their personality but especially Nate will evolve a bit. We look fairly balanced right now but I could handle another male if needed but am not sure how to introduce a new character to the story.
I'm also interested in seeing what the new Stevensen daughter is going to be like. I'm assuming she is close to Kat's age, could be they were classmates at the school where Allen taught, maybe friends before Allen bedded her. Might make for an interesting dynamic but just an idle thought, I don't need by any means.
As for Mei, I'm not opposed to interacting with her but we would likely need some OOC coordination so I know where we are going kink and limit wise. As of now, it seems she is much more interested in female characters, which I don't mind but I can't really help with.