I have four towns (my main town, two themed towns that are complete but that I enjoy playing in from time to time, and a fourth that I am building up but haven't touched in a while). I also babysit my mom's town, which she has all but abandoned.
Lately, I've just been using two of my towns. Each day IRL, I set the clocks back to be within the same in-game day. Towns 3 and 4 are on hiatus (I saved and quit after someone asked to move out in each of them).
The way I've worked on my towns in the past is that I play the mayor character as normal: events, interacting with villagers, etc. The other 3 human characters in each town just earn bells (or receive bells from the mayor), build up their homes, and collect event items. I don't have them interact with the villagers. That saves a lot of time! I have the mayor order and customize furniture for them until they wake up Cyrus and unlock the sewing machine at the Able Sisters.'
As for deciding what happens in each town, I usually just do lengthy events (Halloween, Festivale, etc.) with my mayor in my main town. Tiny events (Groundhog Day, Shamrock Day, etc.) are done by all characters in each town, because there's no time commitment and you end up with a special item.
My main town is loosely themed, and I've played it over 3 years at my own pace. It's my "real" town, the one that feels like home. I've only recently started to get it ready for the Dream Suite. My completed towns are fully themed, and I built them as quickly as possible to complete them for the Dream Suite.
I don't know if any of this helps, but I hope so.