No help here. :#
I have been on a big project for the past five five years.
My two main households were full-house.
I have an orphanage with 8 sims. I also have Uni prep-school with 6 teen sims, a student counselor and an administrator, rotating teens in and out in groups of three. 21 toddlers and their CAS made parents. I avoided playing the parents deeply because playing the toddlers as young adults was the true goal and I didn't want to be tired of any game play features before playing them.
But having so many sims, I couldn't play everyone as deeply as I wanted.
I had Cassandra Goth who was sneaking off to Forgotten Hollow, trying to get Caleb Vatore to turn her into a vampire.
Bella found out and threaten Caleb with death by giant sunlamp, so he nor Lilith wanted nothing to do with Cassandra, but Lilith did suggest a teen vampire that was living at an orphanage. All she had to do was seduce him into biting her.
I did enjoy this story line, following Cassandra experimenting with vampirism, before deciding it was "icky" and cured herself to become a spellcaster, but I skipped over playing out Cassandra's and the teen vampire's relationship.
I also had Cat-sim occults living in the orphanage, but I didn't get to play one of my cat sim's being always up to some mischief with her best human-friend. Nor did I get to play out the story line (In my stories thread) of the cat sims discovering they were sterile when they became teens. My cat sims are illegal genetic experiments, given over to the orphanage because it was isolated on Windenburg's island. The government kept tabs on them and examined them periodically. Once they were discovered to be sterile, they were no longer considered to be a problem. However, the story as head-canon was good enough.
It wasn't until half my original sims were through Uni that I realized what my true project was.
It was to build a master save with my favorite sims, lots, and game play loops all set up and ready to go whenever I want to start a new save. One of my game play loops is the interplay of Style Influencers, Fashion Photographers, and Fashion Models. The game does not have fashion models as a career, so I created my own career and new trait to support having fashion models in the game. I played two models in order to test the career and the new trait. Playing only two sims was very relaxing because I am used to playing 3-8 sims at a time.
And now comes along High School Years to add to all of this.
I played through half my teens, but I have 9 more to go, perfect timing for HSY.
I have enjoyed my massive projects, playing out a few key storylines, but it was a broad, but shallow pool.
Once I have my master save set up, I will only play a few sims and rotate between a few households per save.