Normally there will be a patch when a DLC comes out to deal with problems created by the DLC,
Except in this case the game already has plenty of problems
before the DLC is added. I don't see why you wouldn't run two teams: one team working on the DLC content, and the other working on fixing the game engine and the baseline game content. Or even, if I might be allowed to be so heretical and revolutionary, devote *all* effort toward fixing the game engine and the baseline game content before you think about adding more ingredients to the soup. The fewer the variables you are working with, the easier that bugs are to find and kill.
As far as "there's already been a patch", there's actually been two. The first one was sent out about a week after the game was released, a common symptom of inadequate beta testing. The second patch was released later, and broke about as much as it fixed including the infamous lever action bug (which existed before, but got much much worse). At this point it'd probably be better to run the base game, plus the first patch, plus the community-developed patch, if you could somehow make that happen.