i just put mine together so i'm still exploring, but i do have an idea to cut down on clickiness:
on notes where the decay overlaps with the attack of the next note, there is an audible click when the waveform resets. one way i've dealt with this in reaktor is to set a threshold for the envelope level, above which the waveform will not reset. this might give a slight variations in the attack tone with overlapping notes, but it's much less noticeable than the reset click. this would also make muting a note with a subsequent zero velocity note glitch-free.