If you had asked this question a few months ago, I would have said APT 1 to start with, because it is the closest to a pure bugfix. You could then try the other mods later, once you got some more experience with the game.

Now, however, I need to go with the community-based update. It's a community-driven effort to fix all the remaining bugs and balancing issues in the game that can be fixed via XML-editing. Once it is done, and has gone through QA, it will be integrated into the game by Stardock. You could call it a out-sourced official update.

Well, I played the update for a good eight hours on Thu/Fri and it seems playable to me.

I think Gaunathor was about to get started on fixing it for the campaign, but he wanted to see if the tech trees were done in their current form.

If you have the retail version of the Ultimate Edition, then yes you'll be able to play it.  If you have registered it with Stardock, you'll be able to get updates from either Steam or Gamestop, depending on when you registered.

If it's already been registered (used game) then you will be able to play the update as a mod anyway.

I've registered my game at the Stardock website already and I'm glad to hear that I can eventually download the update from there. However, since I want to play the campaign first, it looks like I need to wait. Thanks a lot for your answers! Also, thanks for  the work you're doing on what sounds like an awesome update. I wasn't expecting to hear of something like this when I made this thread.