The road ahead
There’s plenty to work on here, but there’s an enormous amount more available. first of all, remember that we can construct all sorts of chords (6ths, 9ths, 11ths and 13ths and so on) in any given key. furthermore, there are more scales than just standard major and minor. modal interchange (also known as modal borrowing) extends the concept presented here to include parallel modes (and is used extensively by many composers from ravel to Zappa to Joe Satriani).
So, in the case of C major, we can borrow from not only C minor but C dorian, C Phrygian, C Lydian, C melodic minor and many other scales. for example, dbmaj7 can be borrowed from C Phrygian, f7 from C dorian, and so on. you’ll have at your disposal a huge palette of colours and endless possibilities in chord progressions and melodies. happy learning!