Maybe 4, but it's hard to say. The motherboard might disable pci-e slots when adjacent slots/features are active. Without more research, or even hands on testing, there's no way to say for sure.

That is a horrible choice for a GPU miner motherboard. I can't comment on CPU mining.

On the internet, nobody knows you are a clueless dog.

Risers on e-bay. I already told you how to find out how big of a power supply you need. Different cards need different settings (PITA, you won't be able to figure it out from what I've seen here,) and radically different cards might not even mine together.

Modern cards can suck 200w or more. 750w is not enough. Also pay attention to the risers you buy, there have been some cases of melted risers

Obviously not. But then again, do you?   

You don't need 8x risers, just use 1x.

750W is enough for 4?. You are missing relevant information, which graphics cards? Probably not enough, unless you use cheap crappy GPUs.

you can place 2 gpu-s in that one.
and you will need one pci-e riser 1x-16x.

try  MSI Z77A-G45 for 6 gpu-s or  MSI Z77A-G65 for 7 gpu-s.