The Gateway doesn't actually connect to a TV - think of it as a media server. It does all the actual recording and tuner functions.
Each TV needs a "Portal" box that communicates with the Gateway through the cable. As far as I can tell, they're little more than a "dumb terminal", operating like a streaming media player. With your above setup, you'd need four Portal boxes.
The Gateway can record up to 6 programs simultaneously on its own, regardless of the number of portals.
The Gateway is actually capable of WiFi and DLNA playback (meaning you can stream content off your home media server as well), although that functionality isn't enabled yet.
Shaw's deal right now lets you rent-to-own the Gateway at $6/mo. and each portal at $4/mo, so you'd be looking at $22/mo. for the hardware for your setup.
AFAIK you CAN purchase the hardware outright, and I don't believe there's any extra monthly charge per terminal.
We have a Gateway and two Portals... it works fairly well, although the interface pauses now and then, and the included remotes are hideously laid out. There's supposed to be a new update coming soon for the interface that redoes the whole thing in HTML5, which will supposedly allow you to view your guide and program your recordings via remote computer or through your smartphone.
Good way to contact Shaw and ask them is actually to tweet a DM to @Shawhelp - I got WAY faster response than using their online chat or sitting on hold on the phone.