I 'transitioned' from piano player to accordions as well.

It isn't as much of an advantage as you think (or as I thought).

Basically, it's the layout of the right hand which is the same,
and the skills in playing in different keys which crosses over
(the old black keys and white keys, thing). However, that's
about 30% of the skills needed to play piano accordion.

I think the basic coordination and concepts will allow you to as
easily transition to concertina (English or Anglo) or button
accordion.

What I'm saying is--- being a keyboardist will probably help
just about equally with any squeeze-box. Don't gravitate to
the piano accordion just because the thing under your right
hand looks familiar. That probably really only gives you an
advantage for the first five days or so, because at least
you'll intellectually know where the 'right notes' are.