Knockback still refers to Precision Strike.

Also, when you talk about "weapon attacks" in Weapon Mastery, what do you mean? Manufactured weapons or manufactured and natural weapons?
Weapon Attacks means any kind of attack with a physical weapon, either manufactured or natural as opposed to a spell attack, like Scorching Ray or Orb of Acid. A spell that created a physical weapon would count though, provided it dealt the selected damage type.

Is Tactical Expert meant to stack with Powerful Build and similar abilities? Because I think by a strict reading it does. If this wasn't intentional, perhaps you should borrow some of Powerful Build's language - "one size category larger than normal" (difference in red).
Tactical Expert does and doesn't stack with Powerful Build. It doesn't stack with regard to any of the size modifier bonuses. It does stack with regard to wielding larger weapons, because Tactical Expert does not allow you to wield larger weapons.

When does the Fighter gain Battle Awareness? It isn't given a level either in the chart or the description, and Blindsight at level 1 is... ah... not entirely balanced.
12th level. Fixed.

Does Watchful Blade trump Tumbling? It'd be best to state that outright just to clear up any possible confusion.
It does not trump Tumbling, it just changes the conditions that trigger an AoO. Tumbling is still used to avoid that AoO.

Thanks for the questions.