can i store my itunes, photos, and other files on an external drive and access them if it is connected to time capsule?

There is no single answer to this.

iTunes library can be used from a TC.. or via a USB drive plugged into a TC.. it is slow and may not achieve what you want but is possible.

photos.. meaning iphoto or new photos app library cannot be safely stored on the TC if you use it.. in other words.. store or backup is fine.. start using it and the library will be corrupted. Apple is very explicit.. iphoto library should not be used on a network drive.

photos is of course intended for local computer or for iCloud.. but apple have worked hard to make sure you cannot easily use it networked.. I am not aware of people using work arounds yet or how reliable they are.

If you mean just all your raw photos of course that is fine.. dump photos from the camera straight to the TC is OK..

REMEMBER THIS.

Apple did not build the TC as a NAS.. you are trying to use it as a NAS.. which it looks like,, and feels like.. except for one major obstacle.. it has no backup.. so files you store on the TC.. or on a USB drive plugged into the TC have no where to backup and no application available to back them up. This can be serious. Time Machine cannot backup network drives.