1. The Rattler (extra) weapons. In the base game there is no specific ammo, but they have a special rule that allows you to use the top card of your deck (blind) as ammo (in the video game it has no ammo but uses your resources and money as ammo).
There is an expansion character that does have ammo, but not from merchant.
2. Carja "follow up" - as it says you "move" into the square with the enemy, its not a "sneak" or "sprint" , so won't wake up adjacent enemies.
3. "Follow up" and "Silent Strike" - the consensus is that yes, its badly worded and no, it doesn't work (unless the enemy is in the tall grass), because it says move then attack, so at the start of the attack you weren't in grass.
It does work if you do a normally melee attack and start in grass but 'pop out' with the free move.
4. "Free actions" - these still count for the 'one per turn' unless it specifically says otherwise.
So you couldn't (using Carja as I have the cards in front of me) do a normal melee (and influct a condition) then use Follow Up as you've used you melee action.
You could get a 2nd melee from her level 3 Elemental Mastery trait for example.
I thought there was at least one more question we asked, but I can't recall what it was (make notes next time!).