Once you make your account into a publisher account, you can't go back. But you can publish under different pen names for different things.
I sign into Smashwords with my email address and get my money through Paypal. It's actually pretty simple and there's no reason to be scared. If you need any help, you should be able to just contact someone there and ask questions: @markcoker for Twitter,
http://www.facebook.com/Smashwords for Facebook, and you can always email them directly.