Simply trying to create 2 types of particle systems, one for the simple hair on top, and one for the hair (sideburn area) how can I make the sideburn hair shorter by making it a new particle group?

Create two vertex groups on your head. One called “ontop” and one called “sideburns”. Then add two particle systems to the head. Setup the systems for hair as needed, assigning each one to its own vertex group. Each particle system will have it’s own length.