Currently, I'm just playing the minor pentatonic, major scale, and the blues scale. Should I learn any other scales?
Harmonic Minor and Diminished for metal (they're not as easy of scales to play though)
learn all the modes, ionian, dorian, phrygian, lydian, aeolian and locrian, they help verry much
Depends on you playing ability...major scale is a pretty good technique builder