(dear mod, I hope this is good forum for this topic - if not - please move)

Hi, I use my main computer for mining, I use NiceHash Miner software and I mine ~37Sols/s (i7 + gtx970). After few days of mining I'm ready to invest some mBTC or $$$ to build PC dedicated for mining.

I dont need case/screen/mouse/keyboard, I will buy cheap 4gb DDR ram and cheap HDD.

My biggest concerns are about motherboard, power supply, CPU and GPU.

I don't want to risk big amount of money ( $200-250 ), so for the beginning I'd like to buy cheap motherboard with 4 PCIe slots, and one GPU, and PS and CPU.
motherboard Asus H81M-Plus - $50, 1 x PCI Express x16, 3 x PCI Express 2.0 x1, chipset LGA 1150 (so i3/i5/i7)
power supply opengate 600W - $25 , or I can buy two opengate 400W $15 each - what do you think?
CPU - here I don't know if i5 is enough for 4 GPUs? or should I expect that CPU will be a bottleneck in this build and it's better to spend more on i7 ?
GPU - I found on ebay used gtx970 for $100 and I think that solid 25Sols/s for this price is a good deal - or do you think that AMD is better?


So what do you think about this build? Is that motherboard good for 4 GPUs? How to calculate power consumption for these GPUs? And how to calculate CPU "demand" for each GPU?