Can't believe I just saw this. You can easily snorkel yourself at Sombrero. It's straight out from the beginning of the 7 Mile Bridge. You can see the tower from the bridge. Once you get close, you'll see other boats. They have mooring balls, so you just run your bowline through the loop on the mooring's rope and cleat it. Then hop over. I've been on Looe Key and Sombrero. Looe Key is nicer, but only a little bit nicer. And Sombrero is a 15 minute boat ride from where you're staying. Straight out from Vaca Cut, is Coffins Patch. Another reef with mooring balls. It's a little deeper than Sombrero, so I prefer Sombrero for snorkeling. Straight out from your place, in The Gulf, is plenty of good fishing if it's too windy for the reef or blue. Or, the wind is coming from the south. Set up on the edge of one of the banks and chum. You will get mangrove snappers for sure. In April, you will also get Spanish mackerel. You may also see speckled trout or cobia, sharks and barracuda. In the chum slick, you can freeline chunks of cut bait and shrimp. Always bring a few dozen live shrimp. Everything eats them. You could also put a big cut bait on the bottom for a shark or goliath grouper. I also freeline a rigged ballyhoo, far off the back of the boat. A big barracuda, kingfish, big spanish mackerel or who-knows-what might hit it. If you can get to the reef, use the same strategy. Anchor in the sand and drift your chum and bait towards the coral. You'll easily see the difference. It will be swimming pool clear on the reef. If the wind really sucks, you can fish the big bridge. Fish near the pilings and you'll get snapper, small grouper and jacks. There are also tarpon, permit, barracuda and and sharks under the bridge. If you get a really calm day, find the Thunderbolt wreck. There should be large school of big permit on it. Drift over it with a live shrimp or crab on a small jig head. Get that bait about 30-50 feet down. Permit will willingly bite if they are there. Captain Hook's dive shop does regular dives there and they can tell you what kind of fish are on it at that time. There are sometimes big amberjack on that wreck and always huge goliath. They will take you into the wreck more often than not. Also, if you can tie up on the wreck and chum, there are big yellowtails and other snappers. Plus kings and cero. April has every species there. The wind is your only challenge.
My advice on snorkeling - take your own boat to Sombrero Reef if you can physically do it. If it's way too windy, take the snorkel boat out. Spirit it is called.
My advice on fishing - you can do it on your own. But, if you can go out with a guide on your first or second day, you will have success and learn a lot.
The Spirit snorkel will get you to the reef. You'll be out with a crowd, but you can swim away from them. Definitely do it, though. 
