I never saw your post so sorry for not responding.
If your going to Key West that's one thing if your going to Islamarada/Key Largo that's entirely different, they are about 3 hrs drive apart from each other.
One thing about that area is it is very large, and just about everywhere you want to go is quite a distance. Perfect for your TI, in either area.
We have a house down there, and my wife's company has a store down in Key West so we have to travel down there about 1 wk every couple months year round. I own my own Engineering business so I can work from anywhere. I always take the TI down there whenever we go. Since parking is at a premium down there I typically car top my TI when down there on our Yukon. I usually leave the TI on the roof (locked down to the roof with motorcycle locks), and park in our driveway. We also have a large fenced in compound/pool area between the houses, and I sometimes take the boat off the car and put the boat in there, but it's kind of a pain.
We used to launch at the public boat launch at the end of Simonton street (near Mallory square). The problem there is it is very busy, the current is very strong (6mph) from north to south, so basically if you launch your outback there, it is totally impossible to get back and you will be swept out to sea south of the Island (next stop Cuba), So I don't advise kayaking with your outback in that area. It's a struggle even with a TI without a motor in light winds, or winds from the north. To get back you would have to circle around Tank and Wisteria islands, then approach from the north (a 2-3 hr delay).
We found the safest place to launch is down at Higgs beach. We park in the free parking lot, then roll the TI down to the beach (near the sea wall), we asked and they said it was ok. It's a little bit of a pain rolling over the beach sand down to the water, but it's actually easier and a much shorter distance than any of the beaches in Sarasota.
Higgs beach is nice because it's south of the Island and relatively safe there (mild current). We are scuba divers and snorkelers, and you can basically jump off the boat anywhere south of the Island into crystal clear water and see tons of beautiful sea life, most of it is under 15 ft deep. Just outside of FT Zackary is also a nice place to snorkel, but you can't take your boat into swim areas (you must anchor just outside). Be careful when approaching the corner of the Island left of Ft Zachary (toward Mallary square), as the current gets strong there, and can sweep you into the rocks or out to sea. It's ok to use your outback from Higgs beach, there are always lots of kayaks there, just be careful not to go too far out, and stay away from the point mentioned above, unless your on your TI.
There are Hobie cats and paddle kayaks for rent at Smathers beach (Smathers is east of Higgs beach, near the airport)and you always see several cats out there.
We Scuba dive and often go way out to the coral reefs, but that's quite a haul (about 8 miles) down to the Sand Key area, and unless your boat is equipped with massive sails, motors, FM radio, and all the correct safety gear I wouldn't recommend going out that far, unless your really seasoned and familiar with that area.
You can go out to the Mule Keys (closest key is about 3 miles directly west of Key West) and Island hop and snorkel around those keys, but when coming back make sure to swing north of tank island to end up back at higgs beach because of the really strong north to south current on the east side of key west (in the cruise ship channel near Mallory square).
There is a Hobie dealer just north of town I think on Stock Island, I'm sure there are plenty nice kayak areas north of key west, though we haven't gone up there much. You can launch from Geiger Marina and campground, which is nice. We have also camped at Blue Water campground at around mile 13, where we would kayak in the backwaters up there around Horseshoe key.
Further north Bahia Honda is very nice.
If you go further north we stayed at a nice place called Fiesta Key resort last spring for a week around mile marker 90 (just south of Islamarada), and kept our boat in the water tied to reef balls the whole week.
There is a place called Robbies just north of there where they have mangrove trails, and kayak rentals, if you get a change to go to Robbies, I recommend you get the Lobster Bisque, it is the best I have ever eaten, fun place to just stop and eat, and just hang out and feed the terrapin.
If your a scuba diver then Key Largo is the mecca for diving, and John Pennakamp park would be a great place to kayak or sail from.
We stayed at a Hilton Resort near there, and could have kept our boat on their beach for the weekend, but we were there for commercial dive charters and didn't take our boat along that trip. I don't recommend trying to go out to the coral reefs on your TI, as most are 5-10 miles out, and unless your really seasoned, know the area, and have massive sails, a motor (and 100 miles of fuel on board), and tons of safety gear I don't recommend going out that far (open ocean in the Atlantic in the gulfstream, which is very dangerous and swift (about 5mph current)), next stop north Carolina LOL.
If you car top you can pull over pretty much anywhere on US 1 highway and launch your kayak or TI and just go out, it's beautiful everywhere, and the trip itself down US 1 is the prettiest and most interesting drive in the US, make sure you make the drive during the day because it's a beautiful drive, but do not speed, and at night the speed limit is only 35mph for quite a stretch in and around deer key at night. US 1 gets pretty busy with weekend traffic.
Hope this helps