looking for the minimum rig equipment needed to hook up 5~6 GPUs

I'm not sure which motherboard I need. I am thinking of getting the Intel Celeron, which is the cheapest CPU you can buy. but at the same time, I see these motherboards have several PCI-e slots some are 1x, 16x, 2.0, 3.0, it's all very confusing. As I understand, you need pci-e raisers to convert between the PCI-e versions. However, I'm still not sure with other terminology like straps, 1500,1600 being thrown around.

These are the parts I'm thinking to keep the non-gpu rig equipment low as possible.

Intel Celeron Processor G1840,
SanDisk SanDisk SSD Plus Solid State Drive 120gb (not sure if I need the 120gb)
PCIe VER 006 PCI-E 16x to 1x Powered Riser Adapter Card w/ 60cm USB 3.0 Extension
EVGA 1000W PSU
Kingston 4gb 1600mhz RAM