Just wanted to share photos of my setup of Avalons. I hope you will like it.
I do not know for sure but aren't they designed to be horizontal? Maybe do some searching but I thought the Dr. told people that.
As far as I understand, as long temperature is in right range, it doesn't matter how you place the unit. In fact this is standard ATX case with PSU at the top, so I think vertical layout is fine.
I have no idea but you might want to check up on what minor miner said. I mine (trivially) with a passively cooled video card and it has bent and sagged from the heat and weight in my tower case. Conceivably it could be a mechanical requirement. (Again, I have no idea but for what those cost/generate, I'd be sure to check if it were me).