Congratulations! You can regain enjoyment of downwind sailing. I would use a stanchion mount system. But, I've been on boats that store in the cabin or on the deck. I haven't seen up the mast yet. Jaws up or down - I've been on boats that specify either. Extension? You have to learn this. There are limits for PHRF racing. But sometimes for reaching angles the pole is more like a reaching strut and gets the sheeting angle outboard far more than outboard rail sheeting can. In this case it would not be extended greatly. On deeper angles the pole is extended more, maybe to its PHRF limit, to get the clew out as much as possible. The overall principle is that with a pole you can make the shape of the jib the designed shape of the sail and thereby enjoy the advantage of lift even on a reaching or even broad reaching angle. You may only have a few feet of flow over the luff of the sail but that's still to the good. Then there's wing on wing sailing. If you are sailing by the lee with the pole, you can see a reverse of flow over the jib the see the tell tails on the leach flow backwards toward the luff. That is still lift and a good thing. It takes a delicate hand on the helm and is for lighter winds but without a pole it's not possible.