For the rest of us can you post your progress in this thread.

From what I can understand of datasman's comment, he has 16 in a Yahboom cluster which is just a brand name for a case or rack to hold multiple Pi4s (see the picture in the amazon link). The rest are standalone in their own case.

Acibant has 8 and each in it's own case. Now his link about "building a Kubernetes cluster" puts a different meaning to the term "cluster" and has nothing to do with a physical rack. It's all about Kubernetes nodes and joining multiple PIs to form a production-grade Kubernetes cluster. Multiple PIs acting as one fault tolerant cluster for apps or services like the cloud. The optional hardware suggests a cluster rack or cluster case. This is how we are using the term. Physical plastic hardware.

Your link is also about on building a Kubernetes cluster with the Raspberry Pi.

I doubt you need a Kubernetes cluster.

Look at this link and check "What you’ll need" and "optional" https://ubuntu.com/tutorials/how-to-kubernete...n-raspberry-pi#1-overview
They describe multiple standalone PIs each with a Ubuntu Server image on a microSD card (and more stuff). Later they link them up to form a "Kubernetes cluster".
20 PIs working standalone is probably what you want. I think that's all you need and you're in business. I make it sound trivial. It's lots of work.

There's no need to cluster them. Each one can have its own work queue and do its own processing. This isn't a mission-critical situation where you need a fault-tolerant setup to keep a web application or similar going in the case of hardware failure.

As an aside, please make sure there is adequate cooling, either with ambient airflow across passive heatsinks added onto the chips or active cooling via a mini fan/heatsink combo. I liked the look of this case on Etsy that has built-in fans you can use across heatsinks on the individual Pis. If you don't already have power supplies then you can use a PoE (Power over Ethernet) switch with the PoE hat add-on to get an even cleaner setup using one cable for networking and power.

My apologies mates, I just noticed this thread.
I have 16 RPi's in a cluster and 5 stand-alone RPi's in various cases.
The 16 Pi cluster consists of:

3 x Yahboom Raspberry Pi Cluster Case ( https://www.amazon.com/gp/product/B07K72STFB/...o09_s00?ie=UTF8&psc=1 )
16 x Raspberry Pi
16 x Micro SSD with Raspberry OS
16 x 3 amp power supply w/switches
1 x Monitor
1 x Wireless keyboard and mouse
1 x HDMI cable (From KVM to monitor or KVM to VGA converter)
3 x HDMI to mini HDMI adapters (these are only needed for the Version 4's https://www.amazon.com/gp/product/B0111HRJT0/...o00_s00?ie=UTF8&psc=1 )
1 x HDMI to VGA converter (This is only needed if your monitor is VGA and the KVM is HDMI https://www.amazon.com/gp/product/B078NM7KYW/...o08_s00?ie=UTF8&psc=1 )
1 x 16 port HDMI KVM switch cables included. ( https://www.amazon.com/gp/product/B01H1Q2V2K/...o09_s01?ie=UTF8&psc=1 )
1 x 16 port data switch ( https://www.amazon.com/gp/product/B07GR9S6FN/...o09_s00?ie=UTF8&psc=1 )
16 x Cat 6 data patch cables (mine are 2 ft but size to your needs.)
1 x Cat6 cable (from your router to the data switch)
1 x rack (to keep things tidy)
4 x Belkin Power Strips (I attach these to the outside of the rack and chain them together so there is only 1 to plug into the wall outlet)

I think that is everything. There are ways to do it cheaper. My array has grown slowly over the years and if I did it today I could eliminate some stuff. Mine are hard wired to the Ethernet as some of the Pi's are older versions and kept losing WiFi connections.

Hope this helps and again sorry for being tardy.