Based on this information, is there a way to isolate which feed goes where? I know which one is for the fan, but the other 4 feeds I have no idea. If I were able to identify each feed, could I not wire the bathroom at the junction box so that I can have an independent light switch, and then have a switch and outlet (where the silver box is.. see picture above) to control the fan and outlet?
Based on your information, you would need to pull a new cable with 3 insultated conductors + ground from the junction box behind the mirror to the recepacle location to have a switch for the fan there, whether or not it controlled the outlet.
The "unaccounted for" cable in the juction box probably supplies another room.
To figure out what goes where, you can, with the power off, disconnect them one at a time and turn the power back on. Then, see what doesn't have power anymore. Be sure to keep track of how the wires were originally connected!