I just use Asrock H81 pro BTC v2, cheap celeron G1840, 4gb ram, any 120gb SSD. $90 mobo, $45 cpu, $25 ram, $40 SSD. For PSU, get any gold psu with 6 pcie connectors. Don't cheap out on the psu, buy a good brand like EVGA.
850W psu is sufficient for 6 undervolted cards. But 1000W - 1200W is better in case future coins need more power.
Then 6x Rx 480 8gb, or Rx 470 4gb. Rx 470 for faster ROI, Rx480 for future proof, who knows future miners or coins are better with 8gb cards. I buy half of each card to be safe. Get the cheapest card, single fan or reference doesn't matter. It's not like we are mining litecoin and need the cooling.
If you're adventurous, you can try 7 gpus on Msi Z97 gaming 5. Cryptomined on youtube had a video on this 7 gpu mobo.
I'm sticking with this H81 btc though. If it's not broken, don't change it