The general Polymorph rules state you lose abilities dependent on your previous form, like movement types and such.
You gain what the respective spells SAY you gain. So you if turn into an elemental you look at what elemental body IV gives, etc.
Beast shape and plant shape have pretty long lists. You gain whatever abilities your target shape has, or the spell says, whichever is WORSE. So if you turn into a magical beast with fly 120 (perfect), you'd only get fly 120 (good) because of beast shapes limitations.
This spell allows you to take the form of a wide variety of creatures. This spell can function as...
wide variety != any or all
Since none of the spells it can function as list outsiders like Balor, I do not believe you can turn into one.
Your probably thinking of the 3.5 version which was wayyyyy more powerful.
it enables you to assume the form of any single nonunique creature (of any type) from Fine to Colossal size...You gain all extraordinary and supernatural abilities (both attacks and qualities) of the assumed form, but you lose your own supernatural abilities. You also gain the type of the new form in place of your own. The new form does not disorient you. Parts of your body or pieces of equipment that are separated from you do not revert to their original forms.
Take a few moments to read the Magic section, particularly the section on Transmutation (polymorph). It has 95% of what you need to know about every shapechanging ability in the game, from the lowly alter self to wild shape to form of the dragon III.