I think is your first rig, so my opinion is:
-Be aware "Sophisticated" MOBO that can be a pain, try to use Comercial models with 4 or 5 PCI-e (split your cards)
-Dont use expensive CPU you dont need them, use Semprom or a cheapest 64bit new CPU if exist.
-Use at least 1.5gb RAM for each GPU card, if you have more RAM you can increase TC and avoid HW.
-Dont use a Case, use Open rigs home made is good
-Use Only 24cm Powered Riser, put the cards separately you need air flow
-Buy a big Fan to help air flow in the cards
-Use HD or SSD drive if you can (cheap USB flash are slow, and gonna die any moment)
-I recommend to use Linux, Debian or your_favorite distro, only with X server(_no_ Desktop Env.), ssh server, and AMD drivers
--IF YOU-- dont want to deal with ssh sessions, Terminals, Nano or Vi editor, Compiling Miners, Downloding with wget. USE WIN
Plus, tunning a Rig take from 3days -7days (optimal values)
I hope this can help
P.S.: (Linux)In some MOBO you have to disable Integrated LAN, and use common PCI LAN Card.
thank you so much - yes - I have a valid Windows 7 64 bit license to use on this server