Timo,
I love SW Florida. I live in Kansas, but travel to Florida with my wife at least two times per year, mostly to Sanibela and Captiva (Ft Meyers). I fish there whenever I can. I usually go in April and October--both months seem to bracket the best fishing (from Tampa on south).
If you are going to Sanibel, there is a great tackle store there.
http://www.thebaitbox.com/Inshore fish; I think that tarpon are the trickiest fish of all time. I would hire a guide. Not knowing where in FL you were travelling to I offer the very informative web site below. It contains fishing reports for all of FL. (Oddly, the hotter it gets the better the tarpon fishing seems to get. For example, July is a great month for snook, but not a great month for fishermen.) There are also links to guides and other helpful web sites.
I have always wanted to fish the E-glades or the 10K island areas. Some buds of mine have done the kayak tour.
Water is very clear from Tampa to the Keys. Makes the fishing more challenging.
If you just want poundage, you can catch toady-looking sharks from the beach at night. Be sure that this is okay with the locals as they sometimes do not appreciate the soaking of bloody baits so close to their patios.
Good luck.
http://www.floridasportsman.com/4cast/