2x750 corsair Cx750 or 2x750 CoolerMaster should be fine to run 6 x Rx 56 Vega cards. You will not wait that long though as the price of bitcoin is going down so the altcoins are recovering a bit, a rig of mine with 3xGTX 1060 3GB gpu is giving me 0.0007 btc/day today and it was giving me 0.0005 btc when the price of bitcoin was 7500 USD. So overall I think it is a good investment you are making and good luck to you.
Thanks!
So at this point i'm thinking that 850W should be able to handle 4 cards, and i'll be going for 2x850w so i'll have a bit of extra room in case i wanna add a couple of cards later.
Is mixing AMD and NVIDIA possible or not recommended / efficient?
If you use Nicehash it is no problem. I have a rig I have built for some friends that consists of 1 x RX 580, 3 x RX 480 , 1x GTX 1060, 1x GTX 1070 and everything is running smoothly. It is in an Gigabyte motherboard with the Z chipset, (personal opinion I think the Z chipset is the best for mining) no problems from several months now.