I apologize for revisiting this after 4 months, but I really didn't see any point in starting a new topic. It's really just taken me this long to digest the information.
If I am understanding right, any of the pins, except the VCC, GND, AREF, and RESET can be used to control a servo on an appropriate voltage source, correct? At least that is how I am reading the diagram. So if you needed to connect sensors or anything that needed a separate voltage from the servos, and assuming all of the pins were full, you would need a separate MCU board, correct? Which would mean that for the two boards to communicate, then the TX and RX pins would need to be utilized... I think.
Wow, this stuff is complicated. I'm glad you guys understand it.