There are a lot of options including Homosassa and Chokoloskee but I've only fished for them in the Keys.
If you're interested in the Keys, I'm sure there are other places, but 2 places that have good guides are Sandy and Sue Moret's place in Islamorada:
Online Fly Shop - Florida Keys Outfitters - Fly Fishing School, Fly Rods, Fly Reels, Guided Fishing
And Tony Murphy's place in Key West:
Salt Water Angler
They can hook you up with a good guide and equipment. Just be honest with them about your abilites and if you've never done this before let them know. They should get you a guide that is a competent teacher, and can help coach you through some of the specialized techniques used and give you some pointers on casting those big sticks. It's a big leap from FW fishing and does take a little adjustment. The big advantage you have over someone going out for a 1/2 or 1 day trip is that you have a couple of days and each day will get better as you work out any kinks, and you'll have a better shot of having weather (wind, cloud cover) cooperate at some point during the trip.
It will also give you some time to adjust to the heat. A pair of "sungloves", (the back of your hands will roast without them unless you use sun screen and if you use that you may have a hard time holding on to the rod), some strong spf sunscreen (like Copper Tone Sport that doesn't run in water/sweat) and some zinc oxide (for nose and tops of ears and ear lobes) and plenty of water (not soda).
For what it's worth, there were a number of adjustments coming from FW that i found difficult-
casting- with big rods and heavy wind with a minimum of false casts (2-3), usually starting out holding the fly in your hand (by the bend) with 10-15' of fly line out of the tip and slack line at your feet. It would be really helpful to practice this as much as you can with the heaviest rod you have in the windiest spot you can find. You won't necessarily have to make epic casts, but if you can make some 70-80 foot casts in ideal conditions you have a better chance of getting the fly out of the boat with wind--- and it might just take a 20-30 foot cast with wind in your teeth.
seeing fish- it's amazing how a 6' fish can be invisible right in front of you in crystal clear water 3-5 deep, and how far off a guide can see them while you feel like Stevie Wonder. Polarized sunglasses and hat with a bill are a must. You'll find you'll be able to adjust and will be suddenly seeing a lot more stuff as you spend time on the water.
responding to guides instructions: the whole 10, 11, 3 o'clock (off the bow of the boat) thing and "shoot" vs "drop" sounds simple until fish show up and it turns into a chinese fire drill and you forget your left from your right. A lot of times the guide may tell you to cast well ahead of a fish in order to get it deep enough in current to intercept one, or tell you to cast to a fish in the middle of a string of fish instead of the lead fish in order to get a better angle. And sometimes they might tell you to stop stripping and let a fish pass in order to present the fly correctly to a trailing fish. It's really important to listen and respond to the guide and just use blind faith in his/her judgement. And don't cast at 12:00 or there's a good chance you'll hook the guide. They fight pretty well, but it's usually better to wait for him to spin the boat... It's always a good idea to talk first with the guide about the "audibles" he or she will be using, and to use a couple practice casts to shouted instructions between fish to try and get it down.
presentation- lead fish and don't cross their path by casting beyond them. A tiny fly moving toward a 6' tarpon will scare the bejeesus out of him. Depending on the depth the fish are traveling and the speed of the current, sometimes you'll want to lead a fish considerably to let it get to depth and swing in front of a fish. The guide will tell you where to put it.
Hook set- no lifting of the tip stuff trout sets here- you'll be using a pretty vicious strip strike, "almost as if you were trying to break the rod" to set the hook in the bony mouth by stripping with your line hand and jabbing the rod back and to the side.
line management- it's easy to be stepping on slack line in your excitement, or let it flop over the side in windy conditions, or get snarls in your line that will blow out guides if you hook up. Bare feet or socks (if you're worried about sunburn) will let you feel the line beneath you. Don't put sunscreen on your feet our you'll soon be sliding all over the deck like a greased pig. The guide may also have something like a small barrel for storing loose line on the boat which makes things easier.
fighting fish- You'll feel like you were in a bar room brawl. Fighting big fish usually requires considerable side pressure "down and dirty" pulling low in the opposite direction the fish is heading. If it turns right pull low and to the left like you're trying to flip it over. Dip to allow some slack when the fish jumps so it doesn't fall on a tight line.
BTW, a sign you're doing good is that you'll be making different mistakes --- if you have a fish jump and throw the hook, you may have had a bad hookset, but it also means you got the cast and presentation right. If you fail to bow to a fish and it gets off, it means you got everything else right up to that point.
If you want to get a great overview of fishing techniques Tarpon on Fly by Donald Larmouth and Rob Fordyce is a great read and packed with solid information: Amazon.com: Tarpon on Fly: Donald Larmouth, Rob Fordyce, Flip Pallot: Books
(I fished with Rob for years and he knows his stuff.)
Typically, peak season runs May through June, but there can be great fishing into July as well, and there are some resident fish year round.
Finally, I'd only add that you should adjust your expectations --- the fishing can be phenomenal and everything can click into place, but there are no guarantees, except that there are bound to be moments of frustration, blown casts, broken off fish, uncooperative fish- either not moving through or not eating, and wind. It can be really frustrating when you consider the amount of money involved for a day-- but if you take the attitude that a day out on the flats is magic-- and it is-- and keep an open mind turning to other fish if the tarpon don't cooperate and do your best to enjoy the experience you'll have a great time. And it just may take enough pressure off that you'll throw that perfect cast when the chips are down.