How many GPU should I put in one powerfull rig? 6 is maximum? How much hashrate I can get from 6 GPU? Is it around 120-180 Mh/s or I am wrong?
Hashrate depends on which algo you are mining.
For example if we will talk about ETH/ETC? I read 1 GPU series AMD 470/480/570/580 having hashrate aprox. 20-30 Mh/s, is that means that 6 together making 6*20-30Mh/s = 120-180 Mh/s? I am sorry for my beginners questions but somehow I have to start. I really appreciate any help from you guys
That's correct. The hashrate is per card. The miner software divides the hashing work load among all the cards connected to it and then sends the shares to the pool and you can see an estimate of the total hashrate which is also reported in the miner.