You might not need a double wire set up right from the start. Your early 80's Hobie should have a single trap wire set up. If you are new to hobie cat sailing you probably will be quiet busy even without a second trap setup. (that was at least true for me)

Hmmm women seem to have some trouble seeing the honor connected to an ealey death at sea...
There is a connection (wire to harness) called the "keyhole" system. The dog bone is replaced by a ball on a short stretch of wire - the ball is placed into a keyhole shaped opening on the spreader bar. This system is considered to be more removable in an emergency situation. Not sure if it is class legal.
Harness... I do not think there are a lot of restrictions with the class... I use a hip harness that is intended for windsurfing. I like it for its ease of use - especially when the distances between the tacks are short. On long stretches it is not really comfortable. Stay away from the old style bucket seats...

Performance... Double trap is the way to go... adjustability for heights is a good thing - especially for the crew who has more time to mess with that kind of stuff.

Patrick