I'm still doing horrible with my patience, yet we have new information thanks to Red51.
http://steamcommunity.com/app/…1260#c1473096599330403479
QuoteAs ArcticKitsu mentioned, old worlds will still be compatible after the update, so there's nothing to worry about
You'll be able to change the appearance of your character in the main menu (so your character will always look like this [on every world and every server]). However, this only covers the appearance of your body (male/female, skin color, hair cut etc), of course you can also change the clothes of your character (this will be done ingame, so it depends on the world/server you play on)
Yes, it will be available after the player models update