You don't need to use LiPo batteries, they're popular because of their power to weight ratio.

I'm also pretty sure there's something called a 'Battle switch' for the heavies, I don't see why you couldn't use a relay for a feather, just be careful with the draw, a relay will click 'ON' and draw a good lump of current from the off, an ESC can at least accelerate more slowly to avoid stall draw scenarios, but this is only the thoughts of a newbie, maybe the practice works different to my understanding of the theory.

As for the ripsaw motor, every component has it's pioneer, those saws have some mega chops, could be an interesting result for a spinner.