In my opinion this are the best boards for mining. I have been running 14 cards on them for the last 1.5 years, 15 rigs. I only run them dedicated ,either nvidia or amd, I do not mix them on the same board. Hive OS has been great with both . Also the nvidia rigs I run with 8gb of ram while amd I run with 4gb of ram. Before you install any video cards you want to update the bios to the latest available from the bios menu.Make sure your internet is working and you do not get disconnected while it flashes the new bios. Also I change the settings for the pcie to gen 2. There are 3 places you need to make a change in bios for this.
I do not run the hive os on usb but on ssd’s.
One other change I make in bios is to change the state after power down to power up. This is all you got to do to make them read 14 cards.
For the cpu I run some celeron 3900 and g4400.Both work great , I get more hash on monero with g4400, and hiveos make’s it so easy.
As for the physical connection to the pcie slots it does not matter. You can plug them any way you want. I stay away from the 1x16 pcie slot for some reason, even though it does read all the cards I occasionally plug into it.
For the first year I have been running with 2-3 evga power supplies all connected to the motherboard slots, but for the last 6 month I have changed the set-up to 1 evga power supply plugged in to the motherboard and 2 server psu’s which are connected to the evga psu for on/off. I do not use the additional cable to power the pcie slots on the board (auxpwr_A1,A2,A3), no need.
Give it a try, you will find the nvidia rigs with hiveos run like asics ,weeks with no crushes. The rx series are the same , weeks with no crushes. It is the vega rigs that are finicky, but with time and patience you can make those good as well. Most of my rigs are vega 56/64 rigs and I I find I need to stay on hiveos version 06_01 to make them work. Any time I upgrade from 06_01 to any other version problems arise and rigs are not stable. If you run vega VII you can install the lastest hiveos vega version with no problems.
Hope this helps.