Sorry I forgot to answer the second question! Most decoders wont need you to adjust the start voltage but the idea is to have the loco moving smoothly at it's slowest possible speed. This will vary from loco to loco as some have better motors and mechanisms that others, the MM stuff is top notch so you don't really have to do anything with them.
When you're programming with the Prodigy it cycles through the most commonly used CV's like start voltage, top voltage, acceleration, etc. just for convenience but you don't have to enter a value for them.