at about 2:45 in this video lofileif demos chord progressions using an external package called midi harmonizer:
in the case of your hex max for live setup, you might be able to replace the keyboard with part of a single string, for instance notes on the high e above the 12th fret will not sound, but will change to the desired chord.
for improvisation check out chordjam, it is has some randomization which may suit your users.
ripchord is free and very effective. the humanization settings work well.