i have somewhat done a ajax based jsp coding for checking username availability. It worked perfectly. Though it might have some errors. So if there any please point it out. Now
I guess you need to make your own algorithm for name suggestion.
Like once the user enters his name,surname, birth year,etc. then you can design an algorithm that can take these values and do some processing by combining(concatenating) words or birth year or anything that you want to generate suggested usernames.
Then you can simply return that list to the user.