Uber has always provided servers for hosting your games. But if you wanted to break the 10 player limit, or put a little more juice into late game performance, then hosting your own custom server was the only way to go. And right now if you want to host a Legion Expansion game then you have to have a custom server running the PTE version of the game.
mikeyh has kindly updated the Custom Server Setup guide to make it both easier to use (no more VIM!) and relevant to the latest versions of Planetary Annihilation.
So if you want big games, or Legion games, check out the guide to see what you need to do.