One halyard block to both bails? What? Why? No.
10 or 12mm Endura Braid or the like. It can be really small if you're using a sock because you won't be handling it under load.
Don't strip out the tail. You could strip the cover off the standing part if you have a high-performance boat. Better to not strip the part at the head
block though. So probably no.
The ATN Tacker is a silly thing. Maybe an ATN Tacker is for cruising gennakers? I wouldn't know as I've never used a gennaker
...only real A kites. I let the clew of the A kite fly out ahead and windward of the bow. So the Tacker would be a miserable failure.
If you're using the A kite for cruising it's a big plus if you tell the sailmaker
you want it cut to be stable and easy to fly .... unless you want a hard to trim wild fast thing ....