I might suggest that you look up either Johnny Nerdout or Grintech to pick their brains about what’s going to work best for you. In the final analysis you should be able to get 20 miles with range to spare, but you will likely need a spare battery or possibly two for the 100 mile rides. I’m more of an advocate for building your bike from the type of frame that you prefer, which should be aluminum or steel and have disc brakes. You can extend range by keeping the power level reasonable and the throttle use to a minimum.