So ARM has been touted as the low power low cost datacenter and server solution for nigh on a decade now, supposed to cut the cost of a server by a factor of ten to buy and another factor of ten to run. So now that the ARM ecosystem has had the time to age like a fine milk, what's a good Homelab ARM server platform to buy into? I'm looking for something to run a full fledged VM and/or Kubernetes cluster on. I want to be able to run a few 4 core 8GB VMs at a time on a node, so the rPi is out, as are most of the SBC solutions I know of. I'm also not looking to build up a bunch of 3D printed or CNCd cases to put things that were never meant to be in a rack, well, into a rack. So here's some rough critera:

1. 1U, 2U, or SFF formfactor (Think Project Tiny Mini Micro, small black boxes that can sit two side by side on a 1U rack shelf)
2. 16 cores in a node, though preferably more like 32 threads (With or without Hyperthreading)
3. Easily upgraded with DDR3 or DDR4 ECC RDIMMs off the shelf. I would like to be able to buy some DIMMs and upgrade the RAM in my existing nodes if I decide I want to expand the lab.
4. 10GBE SFP built in OR multiple PCIE slots in the chassis to be able to add in my own PCIE cards
5. Options to run multiple HDDs (preferably 2.5" SSDs though even just a pair of m.2 slots would be good enough for a basic node
6. Under $1000 for a node, though $200-400 would be even better as I want to buy many of them.

I'm sure I'm asking too much here, given the promised price, performance, and power consumption that comes with the ARM datacenter revolution, but it would be nice to start deploying ARM at home now that it's a few generations old.