I don’t know if you had a chance to read my article, but let me say that just getting a breath controller is easy–creating a useful MIDI melodica from it is trickier.
The Arduino hackable has a design problem: no exhaust port. Without one, you won’t be able to do vibrato. However, that’s an easy fix.
I have a lot of the Audio Modeling instruments. Just hooking up a breath controller (and my model is professional) and a keyboard still leaves tons of problems. You will never get the full expressivity of these VST instruments without some additional controllers.
Again, I cover all this in my document. If you have any interest in a MIDI melodica, you should really consider reading it.