But all these layers exist on both sides of a modem. Really the modem is translating between a type of physical/data layer on one side (e.g. twisted pair ethernet) to a different physical/data layer on the other side (e.g. docsis)

IMO shutdown and restart are good ones to add.

I also made one to set volume to 1% which is just about right for listening to something while my wife sleeps beside me.

You can set up WireGuard to only route local addresses to the peer, so you would only be routing dns requests through the tunnel and everything else goes via whatever other interface you have. So performance is minimally impacted in that way.