RE: thrust line on sea planes
The thrust line is above both the center of gravity and the center of drag. A thrust-line set at zero degrees will get leverage and push the nose down. This can be really scary if you abort a landing and try to go around because the plane will dive when you add power.
If you tip the thrust line up a bit, it has a lift component that helps keep the nose from plunging, AND the prop blast puts a little downforce on the horizontal stab when you add throttle, als tending to lift the nose and countering the pure thrust's (zero degree thrust line) tendency to push the nose down. When you have it right, there should be no pitch response when you add or reduce power.
A little extra right thrust is good, too, because the prop disc is running at more of a positive angle to the relative wind, so the right blade makes more thrust than the left. If you get the right thrust correct you won't have to punch in right rudder just as you lift off.