I'm thinking about building a rig.  I have a few questions, though.

MOBO/Motherboard/Mainboard
What does this do, and why is it necessary?  Does the type of motherboard you buy for your rig matter?  Can't you just buy a GPU and CPU card and be set?

RAM
The computer needs RAM to carry out the mining operations.  Higher RAM equals more Mining Capacity?

CPU
Should I just buy the cheapest CPU since miners don't use it?

GPU/FPGA
Which is better, and why?  What is the cost difference?

How do I power, cool, and use the rig?

Thanks!