Best way to set up gpu mining rig?
GPU mining in Bitcoin is simply not recommended nor is it at all profitable. This is the same for all other SHA256d coins due to re-purposing of Bitcoin hardware (which share the same algorithm).

Your electricity cost will be far greater than any rewards unless you are using an ASIC (Application specific integrated circuit) miner, any even in that case you may require cheap electricity in order to make it profitable.

However, GPU mining does exist in other Proof-of-Work coins that have not (yet) been primarily flooded with ASIC hardware. Ethereum, for example, has a relatively fair enough difficulty to make GPU mining viable in specific cases. I recommend using this site to compare graphics card profitability in different coins.

NOTE: Mining Ethereum on a graphics card will require atleast 4 GB of VRAM in order to fit the entire DAG file required for mining.