So I agree with the others, there's no right or wrong way to play rotationally. Just do what feels best!
I currently play with three households in one save file. One is the heir of my legacy challenge, the other is the sister, and the third is the daughter of the heir who's now a teenager and I'm doing a challenge with her. I just rotate whenever I feel like it. I only automatically age the family I'm currently playing with.
One thing I think you should consider is aging of townies. Due to the rotation they age a lot faster than your own sims. So my sim's boyfriend, who she had been dating since they were teenagers, has now died of old age whereas she is still a young adult. In fact, the entire town has pretty much died out (currently at G3) so I'm going to slowly fill it up with new families and probably turn their aging off. This way I can have a lively town and create a ton of clubs and friends for my sims.
