Basically i mentioned a v8 because when you start adding all the off road goodies of bigger tires and what not gas milage will drop with the 6cyl because it is struggling ti move it around, but since a v8 would work less it would be better milage. but the cost of a swap is not worth the savings you get by just gas milage, it is expensive to do any v8 swap. like said you need to get out and see how it does and what other jeeps in your area of wheeling are built like. If you are in the area of wheeling where people are driving the 'mud buggy's' or basically a platform atop a truck chassis with tractor tires then a jeep might not be the best platform. but if your doing muddy trails and not just giant mud lakes then you will be ok.
Honestly, for most cases a tj on 35's and built well for the area of wheeling should be good, and 35" tires require a good bit of upgrades, but to go any bigger requires a lot more done to a jeep. Maybe consider a snorkel for the swampy mud trails that I imagine florida having.
Any accessories are all up to you, but in my opinion a decent start if 35" tires would be suitable would be roughly 3-4" suspension lift and a 1-2" body lift combined with a snorkel for deep water, and any other accessories you see fit to make it yours.
Back to the motor, there is not much that can be done to get more HP out of the stock motor unless you have it rebuilt and stroked to a 4.6L or bigger, or swap a v8 in place. Gas milage will never get better than stock because its a jeep and bigger tires just make the milage go down because it is shaped like a brick.
hopefully some of this helps you with some things to consider
2002 tj sahara 3" lift 35" km2, AtoZ rockers, 8k warn, 4.56 gears, lock-rites front and rear