I think it would work, but you are kinda pushing the limit there for 1 machine,
Just curious though, why would you use a 3480x2160 if you only need 2x1080. You can just send 3840x1080 right?
Same with the other outputs. Would probably slim down your graphics load a bit and make it more feasible.
I have used 3x4k as a test before but haven't tried many layers.
Let us know what you end up doing and how it worked if you get a chance.