3. The "soft close" feature is for both seat and lid. It is a GREAT thing. It only takes a few seconds for it to work. You never have to worry about dropping the seat onto the toilet bowl. Would not want to be without it.
4. This is a good question! I believe the curve of the seat is designed to help position the user to "aim" for the middle of the bowl, so that the projectile lands in the water, not on the side of the bowl.