Looking for tips from experienced miners

Hey guys! I ran into some bad luck with my rig, where I've been trying to sort out a problem that I've been having. I had my rig constiently crash once I plugged in a third GPU. It doesn't matter which GPU it is (I've tried to swap them out) but whichever GPU is detected as 3rd will just drop down to super low wattage and eventually just fail and cause the rig to crash. Tried everything, swapping out risers, PSU's, Cables, Swapping the PCIe Mobo slot for the riser, but to no avail.

So I figured it might be the Mobo, and I saw I had an older BIOS version. Upgraded to the latest BIOS, then all smooth sailing, until it crashed again and the BIOS had reverted to the orginal (oldest) version. I tried to flash the second newest version to it now, and it just completely crashed, and now my Mobo is completely corrupted and the rig won't function at all (no video signal at all when I turn on the computer)

So I figured the Mobo was the sinner all along, and I now obviously need to buy a new Mobo. Problem is, all the Mobo's with 5+ pcie slots are out of stock or 10k dollars to buy. I do, hovewer have a couple of these: https://www.iwill.no/iwill-pci-e-til-4-x-usb-3-0-for-mining-risercard-m-m

Those should give me the slots that I need. With that said, I found a cheap mobo on a local website, that has decent reviews. Model name: Gigabyte H310M H, Socket-1151. Will this do the trick or do I have to pick up some Mobo's with more pcie slots? I figured as long as its a decent brand with decent reviews, It should do okay. Am I wrong?

My other pc parts for reference:

Intel I5 6600 https://ark.intel.com/content/www/us/en/ark/products/88188/intel-core-i5-6600-processor-6m-cache-up-to-3-90-ghz.html

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RAM: Kingston HyperX Fury Black DDR4 2666MHz 16GB (HX426C16FB/16)

https://www.prisjakt.no/product.php?p=4248528

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Corsair RM1000x

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The old Mobo: msi lga1151 z170 pc mate

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I am sorry for the long post, but would really appreciate if anyone could help me out. Sucks to have the mobo give out, as I'm missing some profits for couple of days at least, but hopefully I'll be able to get it all up and running in no time again.

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Thanks for any tips or replies.