create subdomain virtualmin mod

i want to resell my subdomain of my domain name, very similar to [login to view URL] currently I have a server setup with virtualmin/webmin ready, so it would be the best if I can 1) let people check if subdomain name is available (not sold yet), take client info into database (name, phone, email, address) 2) let client buy subdomain name for $2/yr and ask if they want to buy share hosting service, Than and checkout with paypal (using subscription method for annual renewals) 3) system creates user name and password and send to the buyer in email when the account is created. 4) client can login to configure their subdomain DNS, choose to use their purchased spaces as email space or "1-click" configuration for changing MX records to google's free email setup and re-direct clients to google app's free setup page for their emails 5) implement password recovery from Virtualmin Password Recovery 1.5 [login to view URL] for the subdomian name 6) billing system (such as billmin) for checking if the share hosting/subdomain name needs to be renewed. email bills to client. suggestions to make this process seamless are welcome, please tell me if you have done similar work or experience using "billmin" [login to view URL] please tell me more how billmin works out for your pass projects.