Altogether, I'm playing 110 active sims. These are in 36 different households. I rotate through all the households, plus I throw in "extra" plays when a sim is ready to give birth or if I have a wedding scheduled. My largest households have 7-8 sims, and the smallest have 2-3. I used to have several single-sim households, but since I want to keep my game limited to only 36 households, I'm not moving so many young adults out on their own. I'm also having a few young adult siblings room together.
In Sims 2, I played over 80 households, so my Sims 4 game is small in comparison.