should work good.... make sure they are out in the open, or build an open air case

He'll need a new motherboard to support 4 GPUs. Those bump in price.

To my knowledge, the linked motherboard can support 5 GPUs

How does that make sense when it only has 3 PCIe x16 slots? And you have 4 GPUs that take up 2 slots per GPU. It's just not gonna work.

Are you unaware of 16x to 1x risers? How do you think some people are running 6 GPU setups?