I don't think that is a common occurrence for Windows 10 users, not sure what is happening there.

Not supported yet, multi GPU support coming real soon though. Might even be in the Beta through dx12, not sure though. I'd expect traditional dx11 CF/SLI later as that needs AMD and nvidia to do there thing.

Yeah, a lot of the buildings are very flat and then somewhat sunk into the ground. The Nexus is one of the few tallish buildings. One of my biggest problems with it is that there is nothing to hit with the various beams and lasers of the units. If they shoot a factory the lasers will just go to the middle and suddenly stop with no visual reason to why as the factory is flat and has no high walls to hit. It looks a bit odd and I miss the more natural look of things pounding the walls or edge of a building. Of course it is different for ballistics which can hit anywhere and it is OK. 

I think many ask for this

What is your system?

Last night I tried to get as many units as possible to see how it did before crashing. Someone said they got to a logistics value of 18000 which is way higher than I had seen elsewhere. I got to 10,000 before it crashed. that was on DX11. I loaded it up the save game in DX12 but it still crashed around the 10K logistics mark. Frame rate had dropped a bit but other than that I didn't notice any slow down or other graphic glitches (edge of map glitch is there from the beginning). I built mostly T1 so probably had between 3k-4k units (where 4 brutes = 1unit) so not bad. Hopefully a lot better with the Beta.

There is a limit to the number of units that can be selected at once, and there is a bug which occasionally prevents the selection rings from disappearing when deselecting units. This can be perceived as non-responsive units and can make controlling armies larger than ~1K at a time difficult.

There is also an inconsistent delay with using the drag box which gets worse as the system gets under heavier load.

DX12 doesn't support multi-GPUs yet, I don't believe.