For layout aesthetics, I was going to enlarge one bedroom into that office. 

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

(click to enlarge images)

Even if you subtract for RE commission, closing costs and discount the property for a fast sale, you should clear around $50-55k.3 - It would take you around 17 years of perfect tenants to reach $51 k in cash flow.4 - If you invest the $51k in flips, make only 10% per flip, and do two a year, and don't reinvest your profits...just keep reinvesting the seed money ($51k), you could profit over $5k/year...double what you would be getting in CF if you left it as a rental.5 - Now, if you reinvested your profit back into the flips, you would be compounding you profits.6 - 10 years of compounded profits, at 10%/flip...2/yr = over$280k in profit7 - After your accumulated profit reaches the point when added to the original seed money equals enough  to when flipped, you can use just the profit to buy rentals.8 - keep flipping the enlarged seed money.  

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.