The problem with this, is you don't know the extent of the damage concealed behind the walls. 

New walls and closet going up

In most cases, the HOA is responsible for anything outside your walls and you are responsible for anything inside the walls.I would pay the bill to ensure the utility is good, then go after the HOA.

We hired a GC for an exterior back wall stabilization.

It is full of mold and the pipes leak from the basement all the way up into the walls.

Who doesnt run their pex on the outside of walls and cabinets....lol

Specifically the modern style with white stucco walls.

I am also thinking of taking the wall mostly sown between the living and dinning rooms (the two rooms abutting the garage.). 

A BIG advantage of these is that we didn't have to fully open walls or run ducting to place heating/Cooling units on both floors.

I might be tempted to walk my butt into the owner's office -- does that LOOK like a place the owner spends 70 hours a week (lots of personal items on the walls?