I'm kind of an obsessive micro-manager and aspiration-achiever, so 3 is usually my maximum. I usually have a couple and their one child. Sounds boring, but I like intimate families with close relationships. I get so emotionally attached to my sims that I can't handle moving any of my sims' children out, so I just stick to one. I use normal lifespan, btw. I could probably handle a lot more if I played on long or with aging off. I should try it sometime. I'm going to try expanding my play-style by experimenting with challenges. :)