And you'll have new cracks in unexpected places, old cracks that will not close, but instead enlarge.

Now if they use a toggle bolt that''s impossible to remove without enlarging the hole to 1/2" then yes, I would charge those as damages.Exterior concrete walls I do not allow installation of anything without prior written approval.

The kitchen was a BOOM by enlarging it and making it an open concept with light colors to add space.

Since you've mentioned no financial limitations I would maximize the income potential of the property by building the maximum number of living spaces that are allowable and appropriate (for the neighborhood and property), enlarge the existing house, create a living unit above the existing garage, create a multi-unit building, and build a second garage.   1st, I'd look into maximizing the size of the existing home with an eye toward adding one or two appropriately sized bedrooms each with its own bath (this depends on how the home is laid out);  2nd I'd create another 2 bed 2 bath Air BnB space above the existing three car garage with a separate stairway entrance to each bedroom. 

Is there a possibility of legalizing the previous two non conforming units rather than using that space to enlarge the legal units? 

“Here"s your chance to Own the whole block, Enlarge your investment portfolio fast and have good cash flow.

And you'll have new cracks in unexpected places, old cracks that will not close, but instead enlarge.

They're separately metered and both legal, but according to zoning laws (section 12.23) it's not clear that the residential unit can be "added to or enlarged" so I'm looking at converting it to a legal ADU as well.

Perfect , you are one good combo.Nice to know about HD vs Lowes , its fascinating how each chain operates completely differently .Great info .By the way , I just looked up window resizing and apparently , reducing the size was much easier than enlarging, there were couple of good videos on youtube

They might be willing to buy it to enlarge their own property.