What parts should I buy when I buy the machine?

I would recommend at least getting a feed wheel.  When a wheel wears out, the coins double up under and the machine labors or jams to a stop. It’s really hard on the machine.  If yours does this on a Friday you will have one on the shelf, if you don’t have one it can take a week to get it, presuming I’m even available to process orders.   For $10 it’s a good part to have on the shelf.  

Out of the box the machine will have everything needed to sort coins.

There are a couple service parts (wheel and coin cup) and one optional part (extension hopper)

Please review a couple videos associated with these items to understand their use.