Is there anyway to save the iTunes sync and back up/app files to my external hard drive? Right now all the data is saving to my C: drive and it's filling it up on my laptop.
Other than that I can only suggest copy/paste to the ext HDD. If you start changing where iTunes is to save stuff, it gets itself very confused, believe me. I tried to have all my music on an ext HDD, what a nightmare.
In iTunes, click "Edit" then "preferences" then click on "Advanced" near the top there will be a box for the location of the iTunes Media folder location. Click on the "Change" button and browse to you external drive.