In the case of your original video and Flims build, I think none of them used advanced pre-warping to align the panels. I think they used built-in projector keystoning. That would account for the misalignment and blurring issues. You can dial in the corners to pixel tolerance with pre-warping.
You could probably do a bit better with 0.82:1 short throws for the sides and center. Mount the projectors behind the screen and have a lens opening for the side projectors. 0.72:1 lens throws like those GT750's he's using mounts the projectors in the projection area -- which you might not want. The top view is achieved by bouncing the projection off of a small first surface mirror angling it at the ceiling.
Nthusim Plus only does up to 3 displays, but we do case by case exceptions and sometimes non-commercial license Immersaview Warp to home builders at the same cost if the scope of their build requires a bit more configurable options. In a case like this we'd need Immersaview Warp to handle it because of the screen panel count of 4.
Feel free to pick my brain a bit. I have fun designing stuff like this.
