The view out the front of the airplane from the pilot's seat is not from the Cessna 206 used for the outside shots. The view out the front has structural bars along the sides of the windscreen, which the 206 doesn't have.
When Tess is alone in the blow hole just before Finn jumps in. This is the last time she is on the inside edge of the blow hole and dives in. There is no rope seen around her body (her back) as she is diving in. The next seen under water the rope is tied around her waist again.
When Gemma Honeycutt is leaving the Precious Gem on the runabout to go shopping in Key west, Nigel Honeycutt tells her not to be long. To which she replies that she is supposed to meet friends in Key Biscayne for dinner and may be gone a while. Key Biscayne is a village of Miami and lies 165 miles from Key West. This is unlikely because it would take 7 to 8 hours round trip to travel that distance in the runabout and she just flew in from Miami on the helicopter.
Finn uses the Vespa headlight as a flash-light during the search in the cemetery. That would be impossible since that model of Vespa doesn't have an accumulator and the light goes on only when the engine is running.
When Finn is flying the seaplane, the elevator clearly has the training edge down, which would make the plane nose over and dive into the water. When a plane is on the ground, such as blue screen shots for close ups, the yoke would sit naturally forward, placing the training edge down.
The goof item below may give away important plot points.
When Moe is chasing Bigg Bunny in the speed boat, he takes a shot at the plane. A buckshot blast can clearly be seen on the middle part of the plane. Moe then hands the shotgun to one of the crew and dives into the water. A few seconds later, when Bigg Bunny is loading the treasure chest into the plane, you can clearly see two shotgun blasts.