[theprgramerdude]

If you want to know about legality and rules, there's this handy dandy thing called the manual. It will contain everything you need to know, favorite it and search for the info you want.

As for electronics, sensors will be your friend; the reason that factories have become more automated is because computer systems operate much, much faster at simple tasks and operations than any human can. Similar reasoning also applies to FRC robots; sensor systems can and will automate basic tasks, like shooting balls and loading them, and also semi-automate (help human operators) in more complex tasks, like driving around and navigating.

Personally, the most useful sensors that can be hooked up are, in no particular order, and I highly recommend you consider using, are:

Motor shaft encoders, for determining rotation speed
Ultrasonic sensors, for medium-range object detection
IR sensors, for close-range object detection
Limit switches, for close-range object detection
The accelerometer/gyro KoP combination, for tilt and speed referencing (making sure there aren't bad readings)
Camera imaging (many uses)

One possibility that I've considered but never used is a current sensor, which is mainly as a fail safe for small, easily destroyed motors.