[aerohead]

I recommend you begin working on mathematics skills with the calculators at the top of the forum.
You need to know your baseline Road Load power and your target performance.
The rolling resistance and aerodynamics are your variables.
If you're going to drive at posted interstate speeds, then aerodynamics will dominate the design.
If you haven't seen the 2022 Mercedes-Benz EQXX low-drag BEV concept, take a look. And pay attention to how they handled the rear of the car. That's where the extended range is going to come from.