From my understanding it works similar to a phone operator. If PC A is a host and pc B wants to connect, it routes pc B's connection to PC A and vice versa. Just like an operator, it only routes the "call connection" but not the "conversation". If that makes any sense.
You can get a VPN with a decent bandwidth to run, and expand as needed. Buying the WSS code would only be for an established and growing game that is needing more connections than Sierra's own server could provide.
The machine specs needed is based on the number of players you have or predict you will have.