Love this in theory, but can't do it with only 2 ports. I need backup WAN.

A backup WAN can be connected over USB, if it's a backup for graceful degradation when the primary high-speed WAN goes down. USB3 gives you a very decent speed, so if your WAN is not very fast (a typical 300-500 mbps home Internet connection), it can just be adequate.

I need a dmz. ;)