Woah dood! Long post. 8D I can't comment on too much here but I'll throw in my 2¢ for whatever it's worth.
Question #1) I am going to utilize the existing “Hawaiian righting system.” In the past I have always just grabbed the 1/2” line from under the boat to right it. Do any of you crawl up to the top hull to bring the righting line over the side of the top hull...rather than grabbing it from below the tramp? If so, how do you do it (I am only 5’ 5” and 150 pounds soaking wet) and does it provide enough additional leverage to warrant the hassle of using the dolphin striker as a leg up?
Hum. I dunno about the leverage without going over the hull. I'm 6'1 so it just takes a bit of a stretch and I can reach up and grab my righting line over the hull. Of course on my boat my mast isn't sealed really well and took on some water, so I wasn't able to right it without help from a speed boat last time anyway, but my friend's boat righted really easily going over-the-hull. I plan to re-seal my mast this weekend and then test-flip-and-right it afterwards so I can try it both ways and compare, if you like.

Question #2) What is the best trap return system?
I still have the original 1972 shock cord running from one thimble to the other under the tramp. Dunno if that's the best solution. LOL
Questions #5 I recently saw the (new to me) keyhole trapeze ring. Have any of you used the keyhole trapeze system…and what are your thoughts on its advantages and disadvantages?
After reading a horror story about a girl who almost drowned because one of the shrouds got twisted around the hook on her harness and held her underwater after a pitchpole, the keyhole system looks pretty attractive. I'd also like to hear other peoples' thoughts on this.
Good luck with your rebuild, broly! And post pics! Some of mine here:
http://www.JaimeZX.com/Boating