Hey guys - I went to the Disney Merchandise panel and the build-a-droid expansion to protocol droids is pretty expansive.
From what I can tell, in addition to the 21 different heads, there are 14 different torsos.
Plus for each RA-7 type droid that can be made there are the unique RA-7 arms/legs.
I am going to swing by Hollywood studios mid-to-late day tomorrow, so I should have more specific details soon.
I was told by the Disney folks that the droids debut today (Friday) at Hollywood Studios, but will be available on Monday at Disney Springs. I'm here through Tuesday, so I should be able to confirm that.
The protocol droids I have so far (the two Celebration ones) have 14 POA, which is great. I'm hoping the same will be true for the ones you can build yourself.