Hi jpark, welcome to CruiseReviews! Seven mile is a beautiful beach, it can get crowded, but you have 7 miles to select your spot. We walked down about a mile from the drop-off point and had the beach practically to ourselves. There used to be a dive shop right where the boats tender, ABanks, that would let you use their ladder to go snorkeling. It's a good spot right there, wrecks, reefs, fish.
Cozumel, we haven't tried Passion Island. We've gone to Chankanaab Park, Paradise Beach, and stopped at just about all of the beaches along the road when we rented a scooter last year. Chankanaab is my favorite because you can snorkel as well as just hang out on the beach. It is a very clean area, but they do charge to get in. There are coupons on-line, however. It was $19/pp, but I believe they've raised the price again. The cab fare is about $10 to get there.
Falmouth is a new port in Jamaica. I'm hoping that it will erase the problems that Jamaica has had by a few of the locals wanting to make a quick buck. I don't know if it will be a secure area there or not, but they may have done what they did in Roatan with Mahogany Bay and made it secure. If not, please heed the advice of others and go on a ship's excursion or with a group through someone reliable like shoretrips. Jamaica is not an island to do on your own. Cozumel and Grand Cayman are fine. Just be aware of your surroundings in Jamaica (well, anywhere really), don't wear a bunch of jewelry or take expensive cameras or recorders with you. I buy some of the water proof cameras at WalMart. They're 35mm and take pretty good pictures. If one were to be stolen, I'm only out $10.
We're not trying to scare you off about Jamaica. It's a beautiful island, it's just that it is a very poor island. A lot of the locals would give you the shirt off their back to make you feel welcome, but there are those that are just greedy and pushy. Dunn's River Falls is a definite "Must".
Please let us know how Falmouth was when you return. Have a marvelous time!!