The first thing that strikes me is 6' long 2" dia 1/4" wall is too short and too thick a wall. Plus around here tubing comes in 10' lengths I would probably use 10' long by 2.5" dia OD ~2.3 ID (Forespar Spinnaker tubing).

If you are going to fly a reacher and a jib, you don't want much overlap. With attach points at 9', 8',7, and 6' from the crossbeam, you can test the best attach point for your reacher.

I would put bridle lines at 4' and 9', to start with.

Mount the tube to the beam so it can at least move up and down. That way the tube is only in compression.

I would expect the spinnaker tube to break long before your mast falls down.

Above all, get plenty of experience in 5-10 kts before you go out in 15 kts.