I've started to mine using my desktop and have bought a couple of additional graphics cards but the noise and heat is beginning to get to me. So, I think its time to buy a second motherboard/cpu/ram.

Is it worth buying a half decent motherboard and CPU for GPU mining or will any old second-hand combo from ebay do? I currently have an MSI z170A Pro, 8GB DDR4 3000 and an i3-6100. Do I need something similar?
I guess it will be worth buying a motherboard with 5-6 PCIe slots... any suggestions for 'not new' hardware?

Thank you