You’d need 10gb on the nas, switch, and computer, or the transfer speed will be equal to the slowest component between them. But whether you’d get that full performance comes down to the speed of the disk controllers on the nas. You either have to find some performance reviews of this exact nas, or cross your fingers when you test it out.
Corporate network routers do this.
Technically you could do this with an old Cisco switch and a shell script though. The script would ping a known address on the internet from your computer. When it becomes unpingable, the script telnets into the switch and shuts the interface for the current isp and no shuts the interface for the other isp. Very hacky, but it’s what I would do if I were in your situation and I’d use the old Cisco 3750 I’ve got laying around.
That’s an easy way to create a network loop. Consumer grade switches usually don’t support protocols like spanning tree.
What matters is the internet provider’s power.
I’ll give an example. A few years back there was a widespread blackout in California. My neighborhood had power, the adjacent neighborhood lost power for about a week. The cable service (Comcast/Xfinity) runs their lines on polls in this neighborhood, and I could see easily that they run from my neighborhood into that adjacent neighborhood. By the next day apparently their battery backup ran out, and my cable internet went down until that adjacent neighborhood got its power restored even though my power never went down.
If the coax isn’t wired inside the house, you’ll need to either do it yourself or hire someone to do it. Depends on the company and type of home, but the cable company will often just get the cable to a box at the side of your house. You’re responsible for wiring inside your house unless you want to pay them to do that.
I’d start by finding out if they have it wired up outside your house first.
You set up a server running openvpn. You port forward the appropriate ports on your router to your vpn server. You get your public ip from your router. Your friends install the openvpn client and connect to your public IP, which places them on your local network. Then you launch the games as if you were sitting next to each other.
It reduces potential issues if you first set your local network IP range to something none of your friends use on their networks.
Buy your own cable modem. Buy your own router to connect to your cable modem, and use whatever dns servers you want. This saves money in the long run because you no longer pay for the equipment rental.