The landing gear shown is from a wide body or jumbo jet. The Vista jet in the movie is a single aisle 737/A320 series plane not utilizing this gear.
Several characters open their eyes underwater, this is sea water so this would be near impossible to do.
Because Rosa is so small, an adult-sized wet suit would not fit her, but the one she has on during the escape is close to a perfect size.
Despite all of the shark attacks, there is very little blood shown anywhere during the movie. Shark attacks are almost always very bloody, and would be much gorier than what is depicted.
All of the survivors on the plane are determined to get to the surface, thinking that will save them, but they would be vulnerable to shark attacks no matter where in the ocean they were.