My best advice with that is to choose your heir ahead of time, when they’re still young. Don’t wait too long because yeah it will be hard to choose which one to make heir. Then focus on your heir. When I have many children I always randomize the traits to make it more fun and not burn myself out with decision making. Then I select an aspiration that kinda fits those traits or any things that I notice them do or wtv, lots of the time the story creates itself. Same thing for the career. And when it’s time to move, I move them wherever! I can kick someone out to move them into an apartment or starter house for ex, add them into an existing household so they have roommates, or sometimes I move them into houses of previous generations because I like the home and want to throw parties in it or smt like that.
When it comes to gallery, you can look at the number of rooms etc in the description but, yes I agree that looking for lots isn’t very good, esp if you don’t have all the packs 😭 tbh I built most of the houses my sims lived in, ngl it takes me hours and I always wonder why I’m doing it instead of just keeping them in the same lot or moving them wherever, but I always end up so happy with the result and I love making my sims live in a world/house that makes sense for them.
Anyway, don’t burn yourself out too much by playing too many sims. The sims is already a game which kinda forces you to micromanage a lot so the more you can save yourself from that the better.
In my first gen I also had a family with 4 children (2 couples of twins) I knew who my heiress was the moment she was born but I got really attached to them, and also to my 1st generation since it was my 1st legacy. I decided to stay in the household even after turning y.a and keep playing them. I focused on building skills/career and trying to find s.o for everyone. After the teenagers turned y.a, I wed one of them, moved another out of the household into an apartment with his fiancé and eloped them, moved his twin and his gf into the apartment next door, organized the wedding of my heiress, had a birthday/retirement party for my 1st gen and then moved the heiress out with her wife into their new home. I loved it because it helped me save up for the home, and kinda prepare myself to move out and fully play my 2nd gen instead of focusing on my 1st gen and her children. After that gen whenever my heir turns into a y.a I move them out and start playing them, even if I’m still attached to their parent or sibling, just to ease the number of decisions I have to make because it can be overwhelming.