1. A few feet is fine - just tie a red rag on the end, or if trailering at night tape on a red bicycle light or LED headlamp.

2. The cheapest way of resting the mast on the back of the boat I've seen involves a big chunk of expanded polystyrene with grooves cut for the rear beam and mast (electric carving knives work well).

3. The mast only needs to be about a foot above the back of the vehicle unless you plan on some serious 4 wheeling or have it projecting over the back of the vehicle for some distance at a very flat angle (unlikely if you have the mast supported off the rear cross beam).

Happy trailering.

Chris.