Ok, I stumbled across "Preferences" right after I posted this and learned the answer to at least two of my questions. You must Pre-Purchase to edit your skin, and it looks like it is done through the site and now any kind of saved file.
That is not entirely correct. While you technically only get access to the default skin by pre-purchasing you can still download it on the Wiki I believe.
All you need to do is edit the file (char.png) you get to however you want it to look, then if you've purchased the game you can upload it on the preference page which also features a live preview.