Building my first rig... HELP!

Hi all,
I'm building my first rig and I would like to get your opinion on the best parts I should use for the most bang for the bucks. I would like to achieve a low heat/energy consumption but not sacrifice too much on hashing power as possible. So here goes...

GPUs
4GB or 8GB
AMD R9 390, RX 470, RX 480 or ?
MSI, Sapphire, XFX or ?

Motherboard
ASRock H81 PRO BTC
ASRock H97M Anniversary
or?

PSU
EVGA SuperNOVA 1300 G2 Gold
EVGA SuperNOVA 1600 G2 120-G2-1600-X1 80+ GOLD
or?
Dual or solo per rig?

Risers
any suggestions on which to buy and where?


OS
Windows 10 Pro
Ubuntu?

Which mix of components would you use if you are building your rig from the start with the goal of going the farm route?

Thanks!