Jack shaft with fat bike

At the moment i think i might just run the stock cassettte but would an ebike internal geared hub be any better? would it be able to handle the power any better. So if i were to just run the cassette what are the dimensions of the smaller gear would i need to run if the wheel doesnt clear it?
Also what is a free wheel and would it be any benefit to me?

The cassette was the improvement to the freewheel. When calculating a reduction range for you, factors to consider is: Total weight (rider/bike), terrain (% grade of hills), desired speed.