I almost always start with just one sim and no money cheats, and build my way up from there. I like building their house to suit their personality and needs as their family grows. I like to think that I like to play legacies and challenges, but it's rare for me to ever get past a second generations.
I do have a whole note file of ideas that I get for my gameplay, from designing sims around color schemes, to playing a personality type that spans packs and isn't technically in the game. I think my next goal is to play a sim from birth and make them a social butterfly & fashion focused sim. I want them to own a retail store and do the fashion career that game with the get famous patch. Basically, I always find it easier to stay engaged when I have a goal for my game.