Can the vex interrupts pins be used for anything other than the second sonar and quadrature encoder inputs? I've searched all over the internet but I have not been able to find anything about it.

Also, how come RobotC doesn't have an elseif statement? It has else and switch case, but there are somethings that you just need to have an elseif statement for.

OK, my apologies , RobotC does indeed have "else if". I forgot that some versions of C have a space between the two.

Is there any difference between these sensor types: reflection, potentiometer, line follower, gyro, and accelerometer?

The Reflection and Line Follower are pretty much the same. The Potentiometer, Gyro, and Accelerometer sensors all work differently, and have (at least slightly) different drivers for their types.

I was working with an rcx for a class project, and we specified our attached light sensor as a "reflection" sensor. It worked wonderfully. Also, you can have more than one if command. (Saying just in case)