As it reads, the only requirement to use Stunning Fist is that you declare it before the attack roll - it doesn't call for a standard action, for instance. Following that logic, would it be safe to assume that I could use Stunning Fist as part of a full attack action, use it multiple times in a round and even use it as part of an Attack of Opportunity?
Also, damage is still dealt as normal when using Stunning Fist, correct?
Per the feat description you may use it no more than once per round. But yes otherwise you could use it as part of your Full attack or as part of an AoO. And also yes damage is as normal for your unarmed attack.
<snip> You may attempt a stunning attack once per day for every four levels you have attained (but see Special), and no more than once per round. <snip>