I'm sure this has been explained before but I was unable to find a post that spelled it out. What stats change when you wildshape?
Assuming that the creature in question is normally from medium to large, you ONLY change strength, dex, and con if the spell tells you to, you don't apply size modifiers to those (which was a nightmare under 3.5... my wizard used to have his own binder of character sheets)
Your to hit, ac,CMB, CMD, and skills like stealth change with your new size.
According to the beast shape spell it lists the abilities you can gain (movement and senses) plus the attribiute and natural armor adjustments. Is that it?
Pretty much. Also note that the fact that you gain the base land speed for the form is tucked away in the polymorph description rather than with the spell itself.
http://paizo.com/pathfinderRPG/prd/magic.html#transmutation
What about saving throws, hit points, etc.?
Saving throws change if a score based on them changes. For example, using beast shape 1 to polymorph into a small animal gives you a plus 1 dex bonus, and thus increases your reflex save.
Hit points only change if your con changes. (and i don't think thats the case for small to large critters)
Do the attribute and natural armor changes also reflect the possible size change or do you need to apply changes based on your new size as well?
They're two seperate things. You don't "advance" yourself like you do a monster from the book increasing in size. You simply add polymorph like a buff rather than replace your entire character.
Also, when changing into a large sized animal, can it be any animal (only large) or only animals that are listed as large? For example, can I wildshape into a small, medium, large, or huge wolf if I wanted to?
No..
Unless otherwise noted, polymorph spells cannot be used to change into specific individuals. Although many of the fine details can be controlled, your appearance is always that of a generic member of that creature's type. Polymorph spells cannot be used to assume the form of a creature with a template or an advanced version of a creature.
...and yes. Assuming the spell/ability in question allows you access to larger sizes, there's usually a dire version of the animal you can turn into.
Are you sure about not applying the changes for the size of the creature? Under Polymorph in the core rule book it says that
"if a polymorph spell causes you to change size, apply the size modifiers appropriately, changing your AC, attack bonus, CMB, and stealth skill mods. Your ability scores are not modified by this change unless noted by the spell."Does this not apply to wildshape?
-dm
The size changes he's referring to are for scaling a creature up or down, which usually involves modifing physical ability scores. The passage you quoted has it exactly right, except it also forgot size modifiers to the Fly skill and CMD. You also get/take a bonus/penalty for being larger/smaller than your opponent on Intimidate checks.