LML. I actually just finished building half of what you are talking about. My son-in-law wanted a set-up where he could set something on the turntable and rotate "X" degrees take a pic, rotate "X" degrees take a pic, etc. for one revolution.
I used an Uno, Easydriver Stepper Motor Driver and the $14.95 stepper motor on Sparkfun. I bought a used ION USB turntable off craigslist and dismantled and removed what I didn't need so I didn't have to reinvent the wheel. I replaced the DC motor in it with the stepper. It also had a 9V & 16 Volt internal power supply and I was able to find places to mount the Uno & Easydriver inside and connect to power supply. It also has a USB port so I soldered a short length of USB cable inside to plug into UNO allowing capability to reprogramming if desired, but not have the USB cable always hanging out. I wired up a Nikon Coolpix so I could take the pictures automagically. Actually came out really clean I think.
Current operation sequence is basically:
Focus
TakePic
Rotate 18 degrees (no significance, just what he wanted)
Focus
Take Pic
Rotate 18 Degrees
yada, yada, for a total of 20 steps in this case.
I can provide you more detailed info if you like.