Saving money via pre-closure is a thing of the past.
Axis will levy pre-closure charges, I am not sure about Amex but they have been on top of this ever since it started, I wouldn't pull this with them.
I am still at optional investigation section after chapter 2 and it seems enemies are random and not limited, but ammo is. Shotgun is satisfying but since ammo is scarce, there isn't much choice except to not engage. Plus, most of the time, if I encounter an enemy it's much death since running away is not smooth.