Hi, J!
You can apply as an Elsewhere character as soon as you join, and then submit a student application for the character when student applications open on 1 April. Alternatively, you can also have both a student character and an Elsewhere one — there’s no limit on Elsewhere characters, though we suggest you only apply for as many as you can handle.
When choosing a username, you should choose the full name (most use first and surname; some use first, middle, and surname) of one character you wish to apply for. You can create more characters as subaccounts once you join.
Hope this helps!