You will need a LOT of power to run those devices. That will be an expensive Stepper & PSU. Try fitting a pully where the handle goes, wrap a cord around it and hang a weight off of it - it needs to handle worse case.
Your arm is very strong. Making robot arms to move 5kg loads about ain't cheap! You do it without thinking!
I would tend to use a cheap 12 DC motor with a reduction grear-box, and a couple of relays, or employ a small child to peel my spuds.
Check out ebay for say 12V 30 RPM - which is probably too fast 