I have a lot of layers, it works for me but it does make my hair look fuller. Not everyone wants that.
I've always kept my hair in a lot of layers. I don't know that I'd pick a feature and make my hair that length but hey I guess stranger things have worked.
I go by what my hair is curliest at and hopefully what flatters my face. I'm growing out some short layers now so we'll see how long they get. My shortest one is to the end of my nose now.
2c/3a?
Low porosity, medium texture.
http://public.fotki.com/Medusahair/

If it smells good put it in your hair, if it tastes good spit it out!