Given it has been sitting for a while it might be worth getting a guitar tech to do a full setup.
The nut may need a bit of work apart from truss rod adjustments.
Lemon oil is probably the best to use on the fret board. It helps to clean gunk off as well as nourish the fretboard which is probably rosewood.
12 string guitars do not have pairs strung to the same pitch. Only top E and B are tuned the same, the other four are tuned one octave apart so regular strings are not usable