OK, there is a long answer to this, and a very long ansew (kind of the length of several books).
Basically, each of the modes can be played over a couple of different chords, and different chords can take different scales.
If you want a jazzy sound, play a dorian scale over a m7 chord, but in rock it would be more common to play aeolian (the natural minor scale). For dom7 chords, play the mixolydian scale, but int blues you would play the minor pentatonic, as the interaction of the major third in the dom7 chord works well with the minor third in the pentatonic.
As for chords with things like sus4, add9, etc, the best hting to do is to work out what scale smay work yourself for each one. I'll give you a start. An Eadd9sus4 chord is a major chord with an added 9th and 4th. As these notes are not raised or flattened, you asre still playing a straight E major chord, which means you can play E Ionian (major) over it. However, most sus4 chords take out the third, so you could play a dorian or aeolian scale instead - making it a minor scale. The dorian scale has a major 6th, and the aeolian has a minor 6th. You wouldn't play a locrian scale or phrygian (flattened 2nd, which is a flat 9th where you have a natural), and you wouldn't play a lydian (raised 4th, whereas yours is natural). YOu could play a mixolydian though.
As you can see, it's a matter of deciding what notes are in the chord, and what scales they fit over.
Some chords you will find do not fit with major scale theory though, so you then want to look at the melodic minor scale. An example is a min/major7 chord, which has a a minor third but a major 7th.
A dom7#9 is also an example, where it has a major third and what appears to be a minor third, but in fact is a #9. Over this you could play the melodic minor scale a semitone above the chord note (ie a C melodic minor scale over a B7#9 chord).
However, there is another chord that works well over dom7 chords with a major third, that includes a minor third (the #9). That's right, the minor pentatonic. Typically, the 7#9 chord is used in blues, so you can merely play a minor pentatonic over it.
As you can see, there are lots of options. I hope I haven't confused you, but it can be simple if you let it be. It is quite fun,and I hope you can work it out. Good luck. If you have any more questions (say, about specific chords), just ask.
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