SFP is pretty straightforward. Most of the SFP modules you can buy you just connect and they work. For something like that, you would be doing fiber to ethernet hand off at a switch. Then you have pretty much everything run to the switch including router and just VLAN isolate. It’s not super complicated, but if you never messed with VLANs it might be better to go with something pre-packaged unless you’re up for learning.
You could also do a DIY router and run a multi-gig SFP+ network card over PCIe. You still have to purchase a separate SFP module for that, but that is another option.
Moonlight/Sunlight are both really great options. The only problem I’ve encountered with either is that the mouse cursor is encoded into the video stream itself. It adds a little bit of lag when moving the mouse and makes it feel not quite right. Steam doesn’t encode to the stream, so it feels much more responsive. Parsec doesn’t either, but it does not support hardware decoding in Linux so you’re going to be stuck with an added ~10ms decode time.