My self sim is my avatar. While I do have a save file with her in it, I often use her as a tester sim to try new things out. I don't think she looks much like me, though. I am just not good at making likenesses of real people, myself included, lol. I gave her the traits of Loner, Cat Person, and Goofball. As far as my other sims, a few are based on songs, but most are just people I've thought up. I like goofy sims, I like baddies/meanies, I like a variety of personalities in my households. I also like a variety of looks. I very seldom recycle one of my sims as a base for a new sim, although I have done it a few times. For the most part, I start from scratch.
I did use the CAS story mode before and the end result was that he ended up being one of my new favorites. He's so different than anything I would have thought to come up with, so I do see myself using that feature again if I want to make a new sim but can't come up with an idea for something I haven't done before.