WordPress requires that all usernames be unique, so you may run into trouble using the Full Name as the username.
I recently configured s2Member to hide the username field on the registration form. However, the username field is still there (as WordPress requires a username), it's just hidden.
When the user types in their email address, JavaScript automatically updates the contents of the hidden username field with the first part of the user's email address (everything before the @ symbol).
It also appends some random numbers to the end of the username to ensure that it's unique. (You can read all about how to get this working here:
viewtopic.php?f=4&t=15672&p=48910#p49082)
I then have the
WP Email Login plugin installed, which allows my users to login with their email address (so they never need to know their username).
Do you think that would work for you?