I'm building a film scanner using a dlsr.

Here's a picture of the rig so far:

Basically there's a light source, negative stage, negative holder, camera support stage, camera and lens.  I put a negative in the negative holder and slide it using a guide such that I can take a bunch of pictures of the negative at 1:1.  For example, it takes 25 pictures to cover a 6x7cm negative.  The individual files are then combined into one file using stitching software. 

The system works very well, but it's a bit tedious.  I'd like to automate the negative movement using a diy motorized xy stage.  Many of the designs I've seen are for much bigger units, such as for a cnc machine, or units that require speedy movement.  That's not the case here.  Each movement would be only 10-20mm.

I'm fairly handy, and I can follow directions/recipes well, but I haven't worked with arduinos or stepper motors before.  Any advice or suggestions on a good way to accomplish my goal would be very welcome!