I just got a Protectli Vault FW4B to run it on. I wanted something small and fanless. Didn't even realize Celeron's were still made. Been running it 2 years now with no problems. Even that hardware (8GB RAM / 32GB msata) is overkill for home network.
Protectli was nice to buy from, but I do think there's a lot of similar options.
The jest part about Protectli is the Coreboot and they provide instructions to compile your own, so it even feels open.
That said, fully configured with RAM and storage mine cost roughly £600.
Given electricity prices in the UK, and my requirement for an as-open-as-possible software stack, it was well worth it. If it outlasts the EdgeRouter it replaced (7yrs before power circuitry died) I'll be very happy.
That said, my main concern, as a reply to you pointed out, is that I'll want more than Gigabit in that time; my street is getting 10Gb/10Gb in the next couple of years.
Most of the boxes sold here support 2.5G. No mention of Coreboot, unfortunately,
but could be worth asking if they can install it as they already offer OpnSense or other firewall software installation as a service.
Installing it isn't really enough, you want updates. Protectli provide instructions to compile it yourself, so even if they stopped providing binary releases, you could DIY it; well worth the premium for the security conscious in my opinion.
Protectli was nice to buy from, but I do think there's a lot of similar options.
https://protectli.com/product/fw4b/