If will put a few layers of FG tape and resin on the bottoms of the hull, sand, buff then wax will they be protected enough to stay tied to a buoy over the summer?
Just about the worst thing you can do to your boat is to leave it tied to a mooring for more than a day or two. It's bad for the hulls (osmotic blistering, marine growth) and the rig (literally shaking it to death). Figure out anther way to store the boat.
The boat hulls are Red and the deck is yellow, so I'm hoping that buffing and waxing will clean her up. Is this the case even with out having gel coat on the bottoms of hulls and in various spots on the hull sides?
Not sure what you mean here. Nothing will bring back faded gel coat. Buffing and waxing will make it shiny . . . faded gel coat. What you've shown in the photos is cosmetic damage, although the deck ding should be at least sealed up with a coat of resin. It all depends on how pretty you want to make it.
I've heard that re-stringing the trapeze with parachute 550 is the way to go...has anyone used 550 cord?
Before, you said "trapeze" when you meant "trampoline" - so I'm thinking that's what you mean here, since 550 cord is totally unsuitable for a trapeze wire replacement. It's also not that good for lacing trampolines. You want a small diameter, very low stretch line to hold tension on the trampoline. Check out Annapolis Performance Sailing's line section (especially the sale line section) to find something suitable.
I was told to use JB weld on the deck to fill in any missing chunks in the gel coat. Would it be okay to layer with FG resin instead and then buff and wax?
JB Weld is just thickened epoxy - black thickened epoxy. Most polyester resins are translucent, and you can add pigments to them to try and match the surrounding gel coat (which is polyester resin). Use polyester resin for gel coat repairs.