1. I do try to rotate around 5am because I don't want sims to miss work/school. Other than that I have no rotation schedule or anything. I try to keep siblings and friends aging up so that it makes sense. I don't usually cheat, but it depends on the circumstances.
2. I play over 20 households, so that's quite many sims, not even sure how many! Some I play a bit more actively than others. It's all kind of households really.
3. I have played the same rotation since I got the game, so years really. I hardly play other saves.
4. I use all of the worlds. Some neighbourhoods like Willow Creek are more "finished" as I've been playing them longer and have had more time to work on them. Some like Strangerville I have barely done anything with.
5. For me I guess the drawback would be that rotational play is addicting, I would find it very hard to play just one family. Then another one would be that sometimes sim relationships get culled while playing other families.
6. I love variety! Overall though I often end up doing familyplay at some point because I want my sims to have offspring that I can play later on. Then again I also like to give most of my sims some time when they're single living alone to get a better feel on what kind of character they are.