This is one I put together with vim2 boards - you can have all the design info if you want it? Pretty sure vim4 and vim2 are the same form factor? Backplane boards did power via gpio pins so would have to change that to usb c connectors
Also did this one for vim3 VIM3 Crypto Currency Miner Build - #30 by birty that only has 5 boards but the design scales pretty easily as far as you can scale USB hubs - 127 last time I looked