Congrats on not saving any money (or power usage) over buying a Ryzen 5 desktop, which would absolutely murder the Pi4 cluster performance-wise. Better memory bandwidth, AES-NI...for about the same wattage.
Seriously, go look at the benchmarks. For compression, a Ryzen 3600 is TWENTY times faster than a Pi4, just to give one example.
On top of performance you wouldn't have to deal with hardware consoles, slow disk IO, the network config would be virtual and have a fraction of the latency with much greater bandwidth...and 8x8GB of ram is far less flexible than 1x64GB of ram.
You could put the whole thing into sleep/suspend mode when you aren't using it, too.
Pi4s are cool but I'm so sick of people using Pi's because they're trendy and will get them attention, instead of them actually making sense for the application.