Since you use mods, there are more that can fix some of your issues. I don’t know which mod you’re using to make sims stay in world, but I’ve had decent luck with Kuttoe’s Keep Sims in Home Region. It allows you to mark homeless sims for each world, so you can generate townies without taking up apartment space. It also lets you clump worlds together, e.g. Newcrest and Willow Creek sims can go back and forth, but they’ll allow stay out of Strangerville. If I’m misunderstanding what you mean about not having enough space, MCCC lets you change maximum household size so you can squeeze more inhabitants into a lot. You just have to be careful about taking the big families into CAS.
Zero’s Assign NPC’s roles should allow you to give specific NPCs jobs to keep your sims from filling roles.
As of now, there doesn’t seem to be a way to relocate the high school. However, Rex has a mod that lets you choose your classmates, so you could potentially just set up your teens with classmates only from their own world. You could probably also unassign/reassign the teachers depending on which world you’re playing. If it’s really important, you could also store different school buildings in your tray files and swap it out depending on who you’re playing.
I second the NAP idea for drama; adding bags on heads with free love means it will be a surprise when the romance bars start affecting other neighborhoods. Another option is lots of clubs with various sims/npcs. You can set club activities to flirt/fight with anyone or a rival club. If their club hangouts are set to specific community lots, the should automatically gather and start doing club activities whenever you visit.
