I play rotationally, too, because it makes for a nice challenge and like you said, it's a chance to play around with different aspirations, careers, character traits, gameplay mechanics and so on. Currently, I have eight households with I think 19 or 20 Sims total, with one still being an infant.
I started out with just one household, played that one for months on end and eventually decided I wanted a second one. Then, when the kids of the first household started to grow up, I figured they needed their own homes, too, so now the two oldest daughters have their own places.
But like you, I don't want to wait until all the kids are grown up because with five kids, that can take some time. So I added more households: a shared house with three Sims (a policeman, a scientist and an aspiring actor); a young adult couple who just got married and had their first kid; a young adult couple where he is a criminal and overall such a nasty guy that everybody hates him while his wife is well-liked and training to become a lawyer.
Usually, each household gets one Sim week, and usually I switch on Sunday morning around 3 a.m. unless there's a wedding underway or a Sim is pregnant, or when one of my Sims is in college and gets to live on campus.
I have auto-aging off and age them up manually, and a few Sims that are especially dear to me have familiars so they won't die by accident. They all have to work their way up if they start from scratch, i.e. if it's a brand new household. The kids from my main household start out rather privileged after college, though, because their parents are insanely rich and can give them enough funds to buy a nice home.
Oh, and most Sims of those households know each other, some of them have become besties, too 😁
