About 300W, ~7kWh a day, costs me about $80 AUD a month.

Thunderbolt has nothing to do with an integrated GPU.

Proxmox with Proxmox Backup Server will do most of that if you were willing to move of CentOS Stream and onto Proxmox.

I’ve never heard of them but I’ve bought a lot of random RAM before. If they use proper RAM chips like micron, Kingston, hynix, Samsung, etc then I wouldn’t be too worried.

Micron, and Intel would be the ones I would use if you wanted reliability.

If you can find some Samsung enterprise spec drives then that would be ok too.

What 2 drive case with hardware RAID do you have?

The newest version of Proxmox supports some SDN (Software Defined Networking) so that might be of use to you here.

I haven’t played with it yet, so can’t help too much, but might be worth a read of the documentation

https://en.wikipedia.org/wiki/Classless\_Inter-Domain\_Routing

As an alternative to the other suggestions, map out your network in Netbox and let Netbox draw your diagram for you!

Are all nodes dedicated to labbing or do you have some HomeProd services running as well?

One rack is much the same as another. Just depends on the space you have available and budget

OMV extension pretty much just runs this in a container lol

What are you going to be doing on this persistent ubuntu vm?

Yes

What are you going to connect to the LAN side of the pfsense VMs? Are you going to be using your current route for your pfSense WAN?

Buy more RAM

I use MeshCentral for RMM at home.

Try each one and see which you like the most.

Yes, reverse breakout cables exist (SFF-8087 -> 4xSATA)

100%

Proprietary parts is actual ewaste.