I just placed an order for some g4600's. I will see how that works - the rig that had been crashing every couple hours crashed after 24 hours after I turned off teamviewer - hopefully this puts me over the top.
As for power, both are built the same way. Each is running on 2 750w EVGA G3 power supplies. Each SATA/molex power connector is running no more than 2 GPU risers. The molex connectors (and single SATA) hooked to the board each share with the riser for a single GPU (this means 13 GPU's, 2 motherboard molex, and 1 motherboard SATA to connect. The PSU's each have 3 SATA and 1 Perif (molex) connector, hence my using two connections per cable). I did have a 550w PSU in the mix (as a third) to see if that would change things, but it did not.
The only other discernable different is that not all GPU's are the same brand/make (but all are 1060 6GB), and the risers are not all identical (though I have switched them out in troubleshooting).
Good, G4600 is 2 core, 4 threads CPU. That will definetely help, much better than Celerons you have.
As for the mixed GPU's, try to put as many of the same brand/model in the same rig. Then you will have to manualy set overclocking for each GPU. Don't use the global OC for all. Try with the lowest stable value for all (I believe it was about 600 memory for you), then increase +50 memory on one brand/model and see if it's stable, then try +50 on different model and see if it's stable, then repeat until you get max for all models. It will take a while to fine tune it, that's the downside of mixed cards. Good luck and keep us posted.