There are things to look out for here, if you have low power supply like 500 watts it's better to set up two rigs because this power supply can't power up to 6 GPUs, it's better to divide the GPUs on two motherboards, four here and there, also it's less stress work for two motherboards than one motherboard unless the motherboard you are using is made for mining purposes only
I do not agree. And here is why.
Using risers removes all stress from the mobo. 13 gpus on risers are less stress on the mobo than a single gpu plugged directly in to the mobo.
Plus it helps spread out the gpus so they run cooler.
Less mobo / cpu / ram / psu / storage device = less cost and less wasted power. Means more can go into gpus then being wasted on the support hardware.
There is no issue getting multiple psu to work together just some simple rules:
Best to use a Y or W 24pin adapter to sync 2 or 3 psus. If using server psu then use the 4 pin link connection to main psu.
Always power mobo with the primary psu...connect no other psu to mobo unless it is via a Y or W 24pin cable.
Always power gpu & riser pair from the same PSU.
Do not overload wattage on any psu chain or connector. Also known as do not use sata to power your riser or gpu.
And most important if building a rig use linux or a linux mining os...you can run from a thumbdrive and can run on pretty slow cpu...like celerons and pentiums and only need 4gb ram max. Again use the least to get the most.
Of course this is just my opinion from running my little farm.
YMMV
