2 sims is easy, 3 is doable, and I've managed 4 sims lately. I felt pretty smug about that; I felt it was a real breakthrough for me. More than 4 is unwieldy and stressful. In addition, my computer doesn't like large groups (6 +), it gets skippy and slow. It also skips with really large lots.
I've just found out that more than 2 at a time in University is a headache that isn't worth the trouble. I was doing 4, oh, it was not pretty, plus my computer objected to a full dorm. As an added problem, one of the students was a werewolf and kept getting furious. I think she was channeling my mood as I tried to get them through just 1 week, with 2 classes each. :D
I'm still trying to get into a rhythm with rotating families. I tend to get fixated and forget to rotate.