There are a few ways to do it. I firstly, I wouldn't worry about focus planes too much. Most professional projector lenses have a wide tolerance of focus shift, meaning that that if you focus mid-stage, you'll probably be in focus enough, either all the way down stage or all the way up stage.
The second issue is convergence. I disagree that you need different warps at multiple times in the show. You just need to place the projectors side by side and send your content duplicated to each projector separately and manually converge each media item in Watchout. The other thing you could do is set the projectors up in Watchout as 3d stereoscopic pairs and assign each media item at a different "z-depth" depending on how far upstage it is. Watchout will then do the convergence for you.