Regarding brake pads length, why are some short vs long? Given the same brake would long ones have more surface area thus stop better? Improved wear?
Longer wear on both pads and rim. In the early days when MTB had same size pads as road-bikes, it wouldn't be unusual for me to wear out a set of brake-pads in a month. On the road-bike, they would last for years. Larger pads on MTB really help extend the time to replacement.
While total squeezing-force on rim is what generates the friction to slow the bike, the total friction doesn't change regardless of the size of the pads. However, whether that friction is spread out on 0.5 sq.in. versus 1.5 sq.in. makes a difference on the wear at any single spot. Smaller pads will face higher friction per unit area than larger pads for the same amount of total friction and squeezing force.