For email/ftp to be user@domain.com, look in Server Templates -> Default Template -> Mail for domain – and make sure "Format for usernames that include domain" is set to "user@domain".
Also, you may need to look in Module Config -> Defaults for new domains, and make sure "Include domain name in usernames" and "Domain name style in username" are set the way you want.
But I’m not sure if those options apply to new Virtual Server administrators or not, they may just be for users created within a sub-server (ie, email, ftp, and additional administrators). You’ll have to experiment
Also, I’m not sure you can set an alternate default address to use for email to the Virtual server owner. Either the email is sent to the Virtual server owner that Virtualmin creates, or you’d need to manually specify an alternative address.
I think
Though, one way to handle that would be to go into the Server Templates -> Mail for Domain, and setup a default alias when a new Virtual Server is created, that points mydomain@mydomain.com to whatever your server administrator is.
-Eric