Just to echo what everyone else is saying, without question your best bet is to get a guide for at least a day. Two would be better, to get the bugs out, learn to spot and present flies to fish, and get some help with casting--- SW is a whole nuther ball game as far as casting goes, and tarpon will test your gear to the limits if you hook one. You can use the guide's equipment for them, and you'll be sight casting to fish with a 12 weight. You'll be paying for very specialized knowledge of tides, wind, temperature moon phase, and the local knowledge of fish movements. It's by far the best way to get a shot at tarpon. The end of April can also be pretty windy. One thing you might consider is booking some thing around Islamorada and planning to fish the flats- for bones or tarpon. In the event of wind, you could tuck into the Everglades to get out of it and look for laid up 100+ tarpon, baby tarpon to 60, and other fish like snook, snappers etc. It's an awesome experience. There are probably similar options or maybe even better ones in April if you have your heart set on one of the big 3 out of Key West but I'm not as familar with the fishing there
As far as DIY, you might want to adjust your expectations a bit. You MAY have a shot at bones, and there is always a possibility of permit. Tarpon would be a long shot, but you should be happy to throw at anything you see--- jacks, cuda, small sharks etc can be a lot of fun. Bahia Honda and Long Key State Parks have decent flats, and would be worth checking out. Try looking them up on google earth to get an idea of the lay out.
Another idea would be to rent a small boat at a place near Key West, or at Robbies Marina west of Islamorada where you can feed the "pet" tarpon to please the fish gods. It would be a Whaler type thing, not a flats skiff so you'll be limited to fishing channels and deeper water. From the boat you could throw into holes and catch a bunch of stuff, though most likely not bones permit or tarpon--- though it would be the best way to potentially ambush a tarpon on your own. Just try and get a handle on the etiquette in terms of other boats, don't anchor up in front of a flats skiff and screw up the path of fish, and don't expect to go out with a guide one day and park yourself in a rental in the same hole the next. Get a chart for the waters the day before you head out to figure out where to explore-- folks at the rental can point out some spots to try and potential trouble spots, as well as give you some ideas of tide movements ( don't get caught on a bar on a falling tide if you're in the back) and to give you an idea of the channels so you don't run up on a flat, or to pinpoint wrecks, points or humps on the ocean side and landmarks on shore.
In Florida you'll need to pick up a SW fishing license if you're fishing on your own wading or in a rental boat. (You're covered if you're fishing on a boat with a guide.) There are a lot of fly fishing shops down there. Two good ones are Saltwater Angler in Key West and Florida Keys Outfitters in Islamorada and if you want to do the guide thing you might want to consider booking well in advance through them. There is also a huge Bass Pro shop in Islamorada that's worth checking out, but the mojo is better at the fly shops.
As far as gear you want a lucky fishing hat, some spf, polarized sunglasses, and floating line for the flats (add a full sink on a separate spool if you want to rent a boat and poke around out front in the ocean to fish over humps.) and a bunch of flies. You can go crazy with them, but a good all place to start might include some size 1 clousers (tan, chartreuse), and 1/0 deceivers a heavy 3/0 rabbit strip thing for dredging deep water holes, a couple of 2/0 poppers or crease flies as general searching stuff, some 3/0 red and white seaducers for sharks (with some tieable wire leader). Those patterns would cover you for a lot of different things in SW pretty much anywhere. Add some specialized stuff like tan merkins (Del Brown's Permit Fly) in size 2 and 1/0, crittery looking stuff like size 2 heavily weighted white and pink Puffs, and moderately weighted greenish Kwans, anything by Borski in tans and browns for bones and permit in size 2, and some tarpon patterns like toads, and key style ties like Cockaroach, Sand Devil, White Lightening, and Apte 2 in 2/0.
An assortment like that would cover a lot of different situations over different depths, over different bottom colors (light stuff over light bottoms dark over dark as a general rule), and cover you for a wide range of fish on the flats, in back country, and in open water as well as give you a reasonable shot at any bones, permit or tarpon you might run into.
Hope this helps, Good luck.
peregrines
