Need joomla login customization

I need modification on joomla registration. Current site has ability, on registration to choose different usergroups and according to selected usergroup on login it shows different menu. It is working with joomla core registration and Multi usergroup registration. What i need: I need when someone click on registration it will ask only for email address nothing else, an activation link will be send to user same like joomla default system, as user activates the account he will be able to fill up different details like name, user name, select usergroup, and more options for custom defined fields. It is pretty simple one someone is expert in joomla.