Really, really nice-looking nice. I looked at your four step process specifically, as you asked. Couple things:
On step 3, maybe change "I do not have a domain name" to "I do not want my own domain name." Customers without a domain name that do
want one may pick the second choice, and not choose "Please help me to get my own domain name." Have to be idiot proof.
After your customer clicks "Please help.." and enters a domain name, you should really do a whois on the domain name entered. Don't let them think they just signed up for a domain name if it's not really available. They'll be a tad upset once they've already signed up and been billed and they realize they didn't get what they wanted.