How to power 7 GPUs with 1 PSU

I got a good friend of mine throwing me 1600w p2 for good deal and I will be using this to power possibly 7 GPUs. I am looking at the ports on the PSU now and I see only 3 sata ports, and 1 perif, 1 perif/sata ports. (https://www.evga.com/products/images/gallery/220-P2-1600-X1_XL_5.jpg)

Now I have 7 GPUs to power with risers so I am puzzled on how to do this.

First of all, are perif and perif/sata ports all same ports with same voltage as sata ports? so do I technically have 5 power ports?

Second, this PSU comes with 6 pin power to sata (http://imgur.com/a/hpRO4) so should I power 2 sata risers per cable with this?

Third, How about if I connect 2 GPUs directly on the motherboard (then powered by motherboard right?) and get only 5 risers each powered by only one 6 pin to sata cable instead of splitting the power? Would my motherboard be okay powering 2 1070s?

I know this can be hard to understand but please give me some advice. Id appreciate it.

Not sure what mobo do you have in mind, but you probably won't be able to slot to GPU and the use 5 risers. GPU's will most likely block the next PCI-E slot as well.

It all depends on what kind of cards do you have and what is expected output. If you are going after big 200W+ cards with 6+8 you might have a problem there. In general it is not advised to you SATA to power Risers, because the draw can be bigger than expected. Of course it works for many people, but it call comes to your specific setup. Keep that in mind, because if you put too much presure on the Sata cable you can melt the connector and you risk burning down the house.

I usually prefer to use 2PSU, because they always come with more cables and more slots that one bigger PSU. Two smaller ones are also always cheaper.

I use the same PSU and power 7 r9 Nanos with it. I power two risers per sata strand and since the Nanos use only 1 8pin I can power them all from the PSU.

Could you let me know which risers you use and which cables you connect them with?