The tiles I'm referring to are thicker than that. If you're going to use the 1/4 inch stuff you should use multiple layers. This is really to allow the tank to settle on what could be an irregular surface. You could also use Styrofoam sheets, like from a fish box.
This depends on the construction of the tank. Most tanks built in the USA have the sides, front and back extended below the bottom of the tank, protected by some sort of trim. Elsewhere tanks sides are built ON the bottom, protected by trim. I'd imagine that the foam or cork would protect either type but it might need to be thicker on the flat-bottomed tank.
Hijacking??? Obviously this isn't a private conversation. <grin>