A: Yes, when a website is activated, you can add a domain - system will ask for a domain name and if the domain name exists, it'll ask you to update your DNS (park with NS change or simple CNAME update if you prefer), but if the domain doesn't exist, it'll suggest registration.

The price may be different for each "tld" (.com, .net, etc.), but it's ~$20 for most of the domains if I remember well. The price listed will be the same for registration and renew.