One of the big problems with getting hold of dev tools from that era is there wasn’t a lot of stuff that was free. Pretty much all the windows developer tools had a price of entry. This means there’s less chance of being able to find stuff because someone making it available for download would probably be piracy.
They’d probably want to develop with Visual C++ 6 on Windows 98SE for the best chance of success. I think I agree that DX8 is probably the one to target, though there might be better luck targeting an OpenGL (or maybe SDL) version from that era.
Getting decent docs might be hard too as even the MSDN library was a paid for product.
As for networking, I think I’ve seen some projects that port TLS 1.2 to 9x windows, so I wonder if you could bundle a library to enable this. I guess the OS TCP/IP stack is riddled with holes too though probably making this a bad idea regardless.
It would definitely be an interesting project, but I don’t doubt it’s going a pretty frustrating time throughout