Having seen someone else build and tinker with a 7 node Pi cluster it seems like an absolute waste of time. 1Gb/s networking, PCIe 3.0 x1, slow RAM, slow CPU. And with all the hats and accessories needed it’s not that good of a deal.

Getting some NUC-like machines makes a lot more sense to me. You’ll get 2.5Gb/s Ethernet at the least and way more FlOPS as well.

You might really dislike the ESP32 cluster I'm planning right now :P