[sdiy] MonoSynth Note Priority over MIDI

[MTG]

So I'm back on this topic of monosynth note priority again, this time 
how to deal with incoming note data over MIDI. I'm thinking of including 
Last, Low and High note priority as well as allowing the user to control 
if subsequent notes retrigger the envelope(s) or not. This more or less 
mimics the options available from the DSI monosynths.

What I'm curious about, is how many notes do I really need to track 
coming in over MIDI?

Certainly two if I'm going to allow the user to play and hold one key 
and pound on a second one (you know, the Keith Emerson portamento thing 
for instance).  Not owning a commercial MIDI monosynth ... do they 
typically keep track of a bunch of incoming midi notes or just a couple?

I've looked at the manuals for a few and there are no specifics in this 
regard.

GB