I tried numerous different display names but it always said it was either unavailable or invalid, so I can't even get past the first step to create an account and download the game. Any suggestions of what I can do?

Just recently completed the game and I was wondering about any secret create-a-characters in this game, I know Vixen is in there. Can anyone tell me who else is in there and what parts are used (or their character codes) to create them? Thanks.