New Miner Rig Review / Help

Hey everyone..

Like many users here i am also new trying to build my first mining rig, in the last days i have searched everywhere for best setups.. and i really need your help to correct me if i am wrong with the setup or is good to go!

Anyway i still have few questions:

ethOS is the best choice? (as i read on windows is hard or maybe impossible to make it work with 6 cards at once)

Does the pcie extenders/adapters have to meet some specific requirements http://i.ebayimg.com/images/g/GJEAAOxyCGNTLk2G/s-l1600.jpg?

Is it worth to go with R7 370 instead of R9 380x ?

A Motherboard Case Power Switch On/Off/Reset with LEDs Litecoin is a must have?

Best place to find a good rig case?

Solo mining or pool? If pool what is the best one?

Here is the setup for my rig (please recommend if better ideas, i am not a super tech guy at all):

Mobo: Asrock H81 Pro BTC
GPU: 4-6 Radeon R9 380X 4g
CPU: Intel Pentium Dual-Core G3258 3.2GHz
RAM: 2x HyperX Fury Black 4GB DDR3 1600 MHz
SSD: 64g ssd
PSU: EVGA SuperNOVA 1600 G2

How much Mh/s ill get with this, around 100 - 120 ?

What else am i missing here?

Thanks to everyone reading this!!