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.
Just because this level of cringey fanboying should never be tolerated, here is a hurtful fact: Valve has argued in court that they are a subscription service and you do not in fact own any game in your library. https://hothardware.com/news/valve-loses-french-court-battle