Because until recent versions of Windows 11, HyperV and WSL were garbage. It’s actually not a horrible option now. I actually use it as my homelab second “hypervisor” as it is always on anyway and it gives me a second always on server for redundant apps with almost no extra power usage.
DO NOT HAVE AN ELECTRICIANS DO THIS. Installing low voltage network cable is a very different discipline. Granted, some electricians are skilled at both while others will install network cabling just like they install romex.
Also, the most difficult part running network cable will be patching holes in drywall which most electricians won’t do either.
How does your observatory control work? Is it using proprietary analog signals on that Cat6 cable, is it using RS-232 serial, is it running IP, is it using a non-IP protocol but still ethernet?
Are you running out of memory or CPU? ie free -h vs uptime/top? Double up the RAM if you bottleneck is RAM or use the 2 NUCs if it’s a CPU bottleneck. Either way, it might be best to look at simply upgrading the a more powerful server in terms of both CPU/RAM though.
The “best OS” is whatever you like, its really a religious debate. I would say just pick your favorite linux distro. Proxmox is just debian with a fancy gui.
You will need to PXE boot into a RAM disk and then use iSCSI/NFS/CEPH/etc for persistent storage.