Do I need to download anything pre-launch?

Aside from the add-ons I'll use and the actually 2.4.3 client, I've downloaded the ptr weeks ago. Am I good to go?

nah you just need the client, set the realmlist, get ur warmane account which u already have , get some addons to help with things, find a leveling spec for ur chosen class ( or not because with x5 xp any dumb spec will be fine lol) and that's it.

Thanks for the info. I appreciate you.

You can set up addons on any 2.4.3 realm and just copy the account folder / rename character folder to the one you will be playing to get settings imported.