I know that ability scores only change based on the description of beast shape, but what about size bonuses and penalties. For example if I become a Tiny creature such as the Hawk do I also get the +2 bonus to attack/ac, the -2 to CMB/CMD along with the other modifiers or does changing in this fashion only include the effects listed under beast shape?
Yes, you would apply any Size related modifiers to Attack/AC, CMB/CMB, Skill modifiers (such as Stealth), including the effect of reach (for instance, a Tiny creature has a reach of "0").
...which is why it's so damn complicated, and you need to pick a few favorite forms to do the math on in advance.
The pathfinder version is much more balanced. It's just .. complicated.