Most ebike motors have different power modes. My wife has a beach cruiser bike set up with BBSHD with 5 power modes (custom programmed) depending on what she wants. Lowest power mode makes it feel like a regular bike because the added power compensates for the extra weight, mid power modes provide varying level of assist, while the top power mode gives you 30+ mph on throttle alone.

With this bike, she can either get exercise, or commute without pedaling at all.

Kit doesn't really matter when you have that kind of power, weight of the frame, wheels, e.t.c doesn't really matter, and you don't need gears - single speed setup is more reliable, with a thicker single speed chain that can handle the additional power. The only upgrade that I did on hers is just bigger 200 rotors front and back, which with mechanical brakes work totally fine for the weight.