I'm working on a template save right now. First thing I did was give all pre-mades makeovers. They all stay. Then I've filled up houses with sims from my library (both mine and others). There will be very few lots open for randomly generated sims.
I've added a spa and a couple restaurants. I'm keeping: 1 library, 1 museum, 1 gallery/art center (San Myshuno), 1 pool, 1 karaoke bar, 1or 2 lounges, 1-3 parks (most likely the big ones in WC and OS and Myshuno Meadows). I'll keep most of the regular bars, since those are the public lots my sims visit most (my sims don't get out much). The rest of the existing community lots are made residential and kept empty for any future generations.
The biggest problem for me when I scroll through all the households (not the premades)...? What families to play in the rotation?? They are basically all my favs from different saves o.o