You will have a blast fishing in that area. There are many, many different options and I'll give you some based on my limited experience in the St. Pete Beach area.
Since I only took up fly fishing last year, all my fishing in St. Pete Beach was with spinning gear. One of my favorite places to fish is Fort DeSoto Park where I've rented kayaks (United Park Services at Fort De Soto Beach - kayak rentals, beach bike rentals, beach surrey rentals, canoe rentals, beach weddings, sunset weddings, wedding locations, receptions, banquet room, umbrella rentals, beach rentals, chair rentals
) and fished the grass flats in Mullet Key Bayou (United Park Services at Fort De Soto Beach - kayak rentals, beach bike rentals, beach surrey rentals, canoe rentals, beach weddings, sunset weddings, wedding locations, receptions, banquet room, umbrella rentals, beach rentals, chair rentals
). This bayou is very popular with fly fisherman. During my last trip, I caught a beautiful 25 inch sea trout and later, temporarily had something that pulled my kayak into the mangroves before breaking the line. Lots of fun!
The kayaks are well used, but functional. They don't take reservations, so get there early. They have a couple of kayaks with rod holders, but they only are suitable for spinning or casting rods. Recommend you kayak through the inlet (highlighted in red on the map) and then dismount on the flats to fish. Many areas are only waist deep or less, but careful there are some deeper holes.
Not having done any saltwater fly fishing yet, you'll have to rely on advice from others on tackle and flies. #5 and #7 weight gear is definitely too light if you latch onto something other than a sea trout or ladyfish.
Might be a good idea to fish with a guide first, as they will provide valuable guidance that you can later use when fishing on your own. Haven't used them personally (yet) but have heard good things about Big Bear Fishing and Kayak Tours
•Tampa Bay Kayak Fishing Charters
•Barry Grady (727) 742-3202
•Offers only kayak trips, which can be fishing trips or eco tours. Their half day fishing rate is $225/half day for two. One interesting option is their four hour sundowner trip. Another is a kayak fishing trip in the Everglades.
•This company is located in St. Pete Beach