Where are you traveling from? If traveling by plane, most airlines let you take a 7' rod tube. Take 2 or 3 of your own rods. 2 or 3 reels will take up little space and you can buy terminal tackle or a few artificials when you get to Marathon. Then all you have to rent is a kayak, and there are a number of places to rent them.
As for the party boat, never tried them in the Keys, but there is one right at Vaca Cut.
Look at Islamorada for the backcountry guides.