I'm doing my first Arduino project to support a larger Robot project.
Question 1: Is there such a thing as a shield that runs the motor(s) and provides joint position feedback?
Question 2 : Once I've decided on a shield, how do I know which of the shields available will work on my Uno R3?
yes for motors, and maybe/maybe not for feedback.
you will need to read and understand the shield specifications.
Most answers will depend on getting more info on your project
fester225:
Question 1: Is there such a thing as a shield that runs the motor(s) and provides joint position feedback?
I believe what you are talking about is servo control. This is not a easy task, especially not as a fist one. One solution would be to get a drive like this http://www.geckodrive.com/g320x.html. It is operated by step and direction pulses just like at step motor driver but it uses a dc motor with an encoder.
fester225:
Question 2 : Once I've decided on a shield, how do I know which of the shields available will work on my Uno R3?
That depends on how the arduino and the shield communicate. On the most basic levels the shield is controlled directly by the port pins of the arduino. In that you must make sure that there isn't any conflict between pin use. There are also shields that use some kind of serial communication like spi or i2c. In that case there are often selectable adresses