9
Oops, forgot.
If you have a fixed ip address, all you need is the mydomain.com account. If your ip address changes, you'll have to use a service such as no-ip or dyndns. this includes a program on your comp which contacts the no-ip or dyndns site and automatically updates your IP address. So, this would be the order to do things:
1) set up your xsas server.
2) get accounts with mydomain.com and no-ip.com (if needed)
3) buy your domain.
4) have the domain name pointed to the mydomain.com nameservers.
5) if you have a fixed IP address, use your mydomain.com account to point your domain to your IP address.
6) if you don't have fixed IP, use your mydomain.com account to point your domain to your no-ip URL.
i think that's it :)