Having two oars saves some time in the shunt which is more important on the smaller canoe. Mounting them on the windward side means that everything can be controlled without moving from your position on the windward seat. As the oar is mostly unnecessary on windward courses, there is no problem with the blade running in the vortex turbulence of the hull. As a rule of thumb I would recommend that steering oars be approximately one half the length of the canoe. Scaling the steering oar up to larger canoes can turn into real oceanic he-man stuff.
Pacific museums contain huge steering oars that take two men just to lift.
This is all very well on an afternoon sail but not what you want on an ocean passage with your girlfriend. I see steering to be the biggest challenge in making the shunting proa acceptable to a wider range of sailors. The results have been widely variable with some claiming great success and others recommending that I have nothing to do with it. It's a deceptively complex issue depending on hull shape, daggerboards and type of sailing rig employed. So there is still much work to be done before we go on prime time with a 60' proa.