My read on it is, you can take on only the special abilities allowed by Greater Polymorph. It gives a list of lesser polymorph spells it can mimic; they in turn give a list of special abilities you can gain. If the special ability isn't on that list for the type you're taking, you can't get it.
Offensively, PAO works basically like baleful polymorph. At least that's my understanding.
re: creature abilitis, I believe you use the beast shape, etc, spells that it `functions as` to determine the list of abilities you can gain. polymorph spells dont always grant all abilities of the form you choose. (baleful polymorph grants ALL abilities, but also removes your own abilities and spellcasting and imposes the animal INT and Alignment, etc)
re: non-willing, when a spell works as another spell, it is talking about the effect. saving throw lines are a different thing (PaO still has it`s own Save/Target line, not `see below`), and if Polymorph Any Object says the opponent is a valid target who is affected by the spell if they fail the Save, then the spell effects apply.
1 - It's a lot of backchecking, but I would allow any ability granted by any of the spells upon which it is based. Polymorph any Object being based off (Greater)Polymorph, which allows the subject the abilites granted by Beast Shape IV, Elemental Body III, Dragon Body I, or Alter Self.
2 - From the last line of the PRD on Polymorph any object
"This spell can also be used to duplicate the effects of baleful polymorph, greater polymorph, flesh to stone, stone to flesh, transmute mud to rock, transmute metal to wood, or transmute rock to mud."