Can you mix AMD and Nvidia cards on the same PC (when mining of course)?
Also what watt PSU would I need for the (3) 1080tis and the (1) RX480
Running the 1080tis at 80% load only.
I have an EVGA GQ 850 Watt 80 Plus Gold
The Mobo is a ASUS PRIME Z270-AR LGA 1151 and supports Quad SLI
Yes, you can mix cards with AMD GPUs with those that have Nvidia GPUs. It's relatively painless on Windows 7+ if done correctly. However, installing the necessary drivers on most Linux distributions tends to be more of a pain (though still possible).
The GQ line is one of EVGA's lower-tier series, probably done by HEC, so I'd be wary of pushing too far past 70-80% for 24/7 operation.
Additionally, the 850W GQ may run low on connectors, depending on how you configure your risers.