Glad you found the review helpful. Now to answer your questions:
1. We took 1 bungee cord---ours was about 2.5 or 3 feet long. This should be plenty long enough and VERY useful!
2. We booked one snorkel excursion thru carnival for the St. Marteen shipwreck snorkel. It was ok, but snorkeling in St. Thomas at Coki beach was the BEST and only 5 or 10 bucks to snorkel....a much better deal and you do that on your own.
3. Cab drivers are everywhere and you won't have to wait on them...they are waiting for you. Most seem pretty legit. Make sure to tell them where you want to go on the island and get a price up front per person and they'll tell you. They are typically cheaper than cabs here in the states, and usually worth the money.
4. We did the fun pass, but since our flight was delayed and we were the last 20 people thru the port at 3:45, there was NO line left! Our friends however, did fill out the pass and they got to the pier at peak time of about 1:00 or so. I believe it took them about 45 minutes to go thru the lines onto the ship. They said it probably saved them some time, but I think it's worth filling it out in advance no matter what..
You will love the ship and trip. I'm trying to figure a way for us to go back very soon! Let me know if you have other questions!