Since most sus4s don't have a third, this means that they're neither minor or major. They're mainly used as transition chords, so you can pretty much play anything you want over them (as long as it fits into the mood of the song).

By the way, if you try to look at each chord individually you're going to get into trouble. You have to look at the progression/song as a whole and figure out what to play over it and what will sound good. Figuring out major 6ths and minor 6ths and all that jargon is nice, but most of the time it's trial and error.

About your m7th question - it depends on the other chords of the song. Depending on what the chord progression is, you could play aeolian, phrygian, or even locrian.