Cafe Press and copyright

I was interested in submitting some T-shirt designs to Cafe Press that I may want to print and sell on my own in the future.

Can I remove my design from Cafe Press in the future?

What steps should I take to cheaply protect my designs?

Can I just put a copyright sign along with my URL?

Do I need to set up some sort of Sole Proprietorship for better protection?

Have you studied the Cafe Press fine print?