Anybody want to opine on what piano accordion is best for ITM?

No expert ... But I don't think there are ITM-specific qualities to look for. A good PA will have a fast, easy action and a good selection of dry and wet switches. In a small box you want the treble side to cover at least the 2-1/2 octave range from G3 to C6. On the left side, 48-bass stradella seems to be a popular minimum, but the PA players I work with both play full 120-bass boxes.

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Vivat diabolus in musica! MTGuru's (old) GG Clips / Blackbird Clips

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Any makes in particular that have those features?

I'd go for a nice 72-bass (and probably three-voice) Italian box and would gladly trade my old East German four-voice 96-bass for same! (Might add, from a Scottish perspective, that most folk group players I know have probably found their portability/capability sweet spot at three-voice 72- or 96-bass where the de facto dance band standard is four-voice 120-bass, and nice Italian boxes are expensive...)

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Why I teach... and where
Master of nine?

Italian, definitely, for speed. Other than that, it's down to what you like. Listen to the best players and check out what they have (I went for Pigini because two of my accordion heroes, Martin Green and Karen Tweed, play that). The player's style is usually the biggest factor, and it will dominate whatever make their instrument, but it still helps you hear the instrument at its best.
Below is a link to some mighty fine ITM playing by Karen Tweed on a Pigini 72 bass 3-voice with handmade reeds, and Colette O'Leary on a battered old 60-bass Paolo Soprani.

http://youtu.be/O_5g5XAkKTg