In reply to GIRTHQUAKE :
I want to make sure I'm understanding you correctly in your initial comments about the PCI-E risers - you won't connect those to USB 3.0 slots. Each of them will connect to a PCI-E slot, the full length or the shorter ones, both are fine. As for powering them, they don't really power the GPU. The black and yellow short cable you have in your picture will connect to the 6 pin slot on the PCIE riser on one end and a SATA plug from your power supply, which will in effect provide the 75W that your card would normally get if it were plugged directly into the PCI-E slot on your motherboard. This is fine for many cards but for some power hungry ones, like a 1080ti or some older AMD cards, it is advised to avoid using the SATA-6 pin cable, as you can melt the SATA plug and cause a fire. Using a 6 pin power wire right from the power supply into the PCI-E is the safest option. In addition to that of course you'll need the 6/8 pin power connectors at the top of the GPU powered by your power supply. If you have a 450W power supply you can't run too crazy of a card, so be careful. Fortunately with mining one of the first things you'll do is lower the power of your card, which helps with that.
GTX 1060 6GB for less than $100 is an incredible deal. With Ethereum prices being high as they are, those GPUs are going for $250-300 these days. They'll get around 25mH/s on Ethereum each, if I remember correctly. The 1070 should get 27-28 I believe.
Safest way to start would probably be just plug the 1070 directly in to your computer and start mining with it by itself. Get comfortable with HiveOS, look up overclock settings, etc. Give it a day, get a feel for it, then you can try adding cards, although if you're going to run multiple cards you'll need a more powerful power supply. You can find great deals on eBay on used power supplies sometimes. I'm at work so my attention is divided right now but please continue asking questions if I didn't help enough!