If you calculate purchase price (used or new) divided by years of security updates left you end up with used phones not being that much cheaper than new ones per year (unless you tend to break of lose your phone often).
Of course new flagship phones tend to get more expensive every year, which...
It's what I do.
I run raw FreeBSD for my backup holding server. The hardware is ECC enabled and can take SAS disks.
That's about as complete as it gets short of a tape robot.
This isn't good for Linux. The Wine emulation layer that allows people to run Windows software on Linux is the foundation of the Steamdeck. Many important improvements to the Wine project come from Valve.
It is hard to imagine that MS as an owner would continue this.
I am sure they would be very happy that the handheld is based on Linux...
I think such a takeover would put a dent into Wine development compared to how that is going now.
Your plan in the first post is doable. I can't help you with Windows to set up the routing, though. You probably also want a dhcp server on that central machine.
And transfers between 2 machines that are not the central one could be slower going through the computer instead of through a switch.
That creates a single point of failure and you have to tell all those computers all the routes (unless you want to go all the way and run a routing demon).
I would hook up everything except the internet to one 10 Gb switch that can talk 2.5 Gb.