... but my concern was that since I will be working with WORD data, the result of the addition could get big enough that I would have to use LONGs...
Using a 10 bits adc, the maximun number you can obtain is 1023. Now summing up 8 readings of 1023 each, you will end up with your word variable at 8184 (overflow will occur at 65K)

Since you are using adc , you have to remove
Code:
INCLUDE "AllDigital.pbp"
from your code.

Al.