and I have no idea..despite a long post, you actually haven't said what is wrong... all you say is
and yet you don't show the compilation error?
Ive no idea what this even means...
Did you look at the demos, Library->Demo->Synth ->MPE -> bounce for example
the concept of polyphony is very simple in axoloti (and MPE)...
for polyphony you need 'copies' of each object for each voice, so... rather than putting in the main patch (which means only one voice) , you copy your entire voice patch into a subpatch (patcher/patch, so its embedded)
(copy n paste is supported , so this is trivial)
then for the subpatch you just need to edit the patch setting to mark it as polyphonic, this lets the Axoloti also know how to route voices , so if you want MPE you select Polyphonic expression (note: this is only useful for MPE controllers, if you want normal polyphony i.e. one channel, choose polyphony)
then close the subpatch, and make sure you hit update .. then you can select the number of voices
the other reason for this patch + subpatch structure , is some things you dont want per voice e.g. FX, so you use the parent (main) patch to add these to the per voice output.
its a pretty simple system, and also not much different to say how Max does it (with poly~) and also PD 0.47+ (with clone)
as for Midi Expression (MPE), you can read up about that... its basically Note+PB , Y = CC74 Z = channel pressure.... mod wheel plays no role.
not sure if anyone has time to write a guide, if not, I hope this will help.