Your username has no effect on gameplay and it not seen by other users. It's only to login. The E-Mail address is your account one, you can choose to also have a public E-Mail address, use the same, or not have a public address. Passwords of longer length with special characters like $ or ^ and similar are better.

Username:	5-25 in length with a-z, or A-Z, or 0-9, or _, or - in your username.
E-Mail:	6-35 length with a-z, or A-Z, or 0-9, or ., or _, or - then a @ with a-z, or A-Z, or 0-9, or ., or _, or - then a . followed by 2-4 letters from a-z for your e-mail address.
Password:	6-24 length of a password.