So if I'm starting from scratch, I'd want to buy a Lee Collet Die, a body die (does Lee make these?), and the seater of my choice?
I'd say that as long as you understand how it's all to be used (not sure exactly what you mean by "starting from scratch"), then YES. The Lee Collet die, a Redding Body die, and a good seater will do all you need to do. For a good seater I personally choose and recommend the Forster Benchrest seating die. It's certainly every bit as good as the Redding version (if not better), and much less expensive.
As far as I know, among the major manufacturers only Redding offers a body die
