As for staying in past, im not that much afraid for SW part. I have all toys mirrored. What worries me is the HW part. Those scrapyards where I get pretty decent HW will eventually run dry. And we know what new HW is...
The biggest hindrance will be, as ever, drivers. They are making consistent progress with USB and PCIe from what I can tell in the Discord. If they targeted a known platform like RPI4 and got all the drivers for that right it could be big.
For a Minimal OS on an Old system, you can try NetBSD or OpenBSD, i386. Modern Browsers will be a no-go, but you will find NetBSD and OpenBSD very usable.
One note for OpenBSD, if you have less than say ~2 gig of memory, you may need to disable the kernel re-link. It will work, but will hammer the system. For NetBSD, I have it on a system with 512M and it works great.
Both fully are able to handle the 2038 issue on their i386 builds (32 bit) and has been able for a while. That is something you should be aware of for long term use.
As for RAM, well I have 16GB RAM and its pretty much upper limit Win2003 can handle. Ideal seems to be 8GB because you will have more Pools and PTEs. For todays web, limiting factor is per process 2GB limit (or 3GB on Linux). It barelly enough to browse using new FF browser. Older browsers like Palemoon are much more memory efficient. When it uses 300MB of RAM, its already quite a lot for it.
I sometimes run two VMs at 512MB each on my 4GB Windows 10 laptop. And I can use Windows apps too at the same time. (VMware workstation.)
If you want to shrink the kernel and the relink memory footprint, @unangst has an unofficial recipe.