I fly out of JGG a fair amount (do biplane rides there in the Waco). It is a nice quiet little airport with a great restaurant. I don't think there is any need to call ahead to reserve tie-down space (plenty of tiedowns on the ramp - not crowded), but you should call in advance to ask about rental car arrangements. I don't think they have any cars on site, but with a call ahead they should be able to have the car there for you.
Other things of interest: relatively narrow runway. Little bumpy, but nothing to fear. Lots of tall trees next to the runway, so if there is any wind, expect some turbulence off the trees and be prepared to go around and try again.
I have honestly done more go-arounds at JGG than any other airport, but flying a 1930's biplane has a lot to do with that. In other words, don't worry/sweat it, but be prepared.