Hi BrianBot,
Welcome and good luck for your project 
Looking at your shopping list, I have the following comments:
motor controller shield:
This device will definitly not cope with the amperes needed to feed your motors :-?
Look here (initial post)
motors & wheels:
The wheels are wide and soft, which is good for balancing
Wheel diameter could be higher
You need encoders (at least one). How will you afix them ??
My instructor seems to think there will be problems with different torques of each motor.
How much validity is in that?
This is addressed with the second encoder
Feel free to document you project here
This thread is now very visible from Google, this is convenient for discussion with non Arduino jerks