Yes, that seat is recommended for the toilet.
Yes, any Toto elongated toilet seat will fit a Toto elongated toilet bowl.
The SS154 backing is more modern that has a smooth edge all the way around, while the SS114 has no back connection to each hinge.
Yes it does.
Yes, according to TOTO this seat will have a small amount of movement in the hinges. This is to ensure the soft close feature works correctly and doesn't hang up and prevent the seat from closing.