This has been my plan over the last few months! Finding a cheap PCIe 4 motherboard + CPU with many slots has been a challenge. Need PCIe 4 or else you’ll quickly saturate your bandwidth. Even with PCIe 4 - you still can. The fastest (affordable) network solution means using 10 GbE - which can be saturated by just one modern gen NVMe SSD :-/
> The fastest (affordable) network solution means using 10 GbE ...
That's one of those "it depends" things. If you only have a small number of computers that need connecting, and you're ok with using 2nd hand gear... then 40GBe Mellanox adapters from Ebay are pretty affordable. eg stuff like this (there's a bunch):