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

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!).