Well you misunderstood. The 5 email accounts are for your hosting accounts, which are under the format of *emailaddress*.*sitename*.mysidiahost.com. You can use these emails as system emails, they have nothing to do with the adoptables site, its associated with your hosting account.
You can change to your own domain so long as you have the domain from a domain registrar. You dont need to have a premium hosting account, although premium hosting account will be necessary once you have a larger site.
