It should work this passenger carts too, not just chest carts. That way you can carry around your injured friend on your dog-sled, while you direct your dogs back to base! Or you can actually trap pigs inside the minecart, and then roast the pig over a fire after bringing it to your camp.
YES! But it should become less minecart-like after put down.
Yes, More woodish than iron.
And meaby some kind of way to control it to? Maby if its having a pig in front the player will be able to ride the pig and if they were controllable you can move it where you like. And that gives a use to pigs in sadles.