Im rather new to all this mining stuff and would like to learn more so i have a few questions i would really appreciate getting some help to learn more about. My plan is to setup a x6 GTX 1070 mine but is it possible to start off with like 2 of them and add more after time? also what PSU is recommended for that? In the last topic someone told me i could run them on a EVGA SuperNOVA G3 80 Plus Gold 1000W if i downvolted the cards but i don't really know what that means, will it effect the efficiency? Maybe this is obvious too you but keep in mind that im still trying to learn! Thankful for the help =)
you can start with one gpu or 6. what ever fits your budget now.
I would recommend going for the larges PSU you can afford as most of your problems will be due to power.
The thing is that 1070s can use very little power or a lot(200W). Depending on what you mine. If you find a coin that is really profitable then you don't want to have to limit your self because the PSU is underpowered.
In a perfect world, you should run a PSU at 80% max. If power cost is a driving factor. And with Return on Investment sitting at +5 years it is. Then you might want to over-invest in a platinum psu.
In short, you need about 1700W as you will be using max 1200W for the GPUS and 100W max for the system. Two 850W should work but my go-to PSUs are the Corsair RX1000. Two of them in the system and you will not have any problems.
But that said just buy BTC or ETH now and don't wast your time.