Intel/Win applications - NUC, MiniPC, Server. What do you recommend?

I would argue that any solid hardware can be used without problems. I am an old gamer/hardware/overclocker nerd and always buy my components considering price/performance/noise/tuning. A few years ago, I completely replaced my then computers. An i5 3570k on the Asrock z77 extreme 4 motherboard, powered by a Bequiet Dark Pro 10. This setup has now been running as a server for 5 years. I locked the CPU clock to the minimum, reduced the voltage accordingly, and did the same with the RAM. Two SSDs and 3 HDDs are connected to the server. The HDDs serve as a data dump. Windows Server 2016 runs on the machine. Applications include Active Directory, file server, media server, Windows deployment, the Unifi controller, PRTG network monitor, and VM Ware for experimenting. It runs around the clock, 24/7/365 at about 40 watts. Of course, a NUC consumes significantly less, but you first have to offset the acquisition costs.

The applications you mentioned don’t require much power. If you don’t have a NAS yet and want to get one, you could run a VM on it. That’s how I do it, for example, for a few things.

I still have an HP 800 G2 Thin Client with i5, 8GB RAM and 256 GB SSD lying around here. I think I will use it for now and then tackle the topic again with the NAS and VM, that seems sensible to me.

I am using two Dell R210 II... one as a pfsense router and one as a server for everything. Quiet, energy-efficient, 1U in the rack. Runs perfectly with Proxmox.

Brief feedback:
I now have the HP Mini PC running in the rack and can remotely tinker around in the ETS from all Macs without any problems, just as I wanted.

I just regret that I struggled with Bootcamp for the last few months and didn't come up with the idea earlier...

You don’t need any extra server hardware for that. If you do proper backups, I don’t see any problems. Most likely the hard drive will die, the rest will run for years. Home Assistant on VirtualBox is a bit tricky. As long as you don’t want to pass through USB sticks or similar, it’s fine. Intel NUC (possibly used) and then Windows on it. No idea if there’s [Gira Projekt Assistent] and [ETS Professional] for Unix!?