Using WordPress as a registration site for events

Hello,

I am currently using WordPress for an event registration site. I use Gravity forms plugin as the actual registration portion.

I need to find a way so after an attendee registers, they get a username and password. After they get this username and password I need them to be able to go back to the registrations site, login, and see their registration form (populated with their prior answers), and be able to update their fields themselves.

I am not married to Gravity Forms. They are easy and reliable, but figuring out this new system is far more important.

Thanks