Thank you for getting back to me! As for the abilities:

Since performing Sunder is actually a feat that years muscle, it takes him some time to recover. So, perhaps once every two days in universe? If used any sooner, it has the potential to tear tendons and cause long lasting damage.

Keening is different, in that it relies on speed and concentration to be executes properly. Using it too often makes him ineffective in combat. Perhaps as a guideline, once per day.

Your guidance is definitely appreciated. Thanks!