Generally, you do not want the county to inspect and tell you what is wrong as you may open a Pandora's box of fines and fees.Some people just punk ADU's  in and don't worry about the permitting but that approach may open you up to legal issues. 

Does the architectural style of the house lend itself to just doubling down on the mid-century modern aesthetic?

I’m here to learn so maybe next time you should offer advise before being a punk.

People will may more for less maintenance and aesthetics as they down want to spend the money to fix it up themselves. 

As builders we need to keep our costs as low as possible with giving the most energy efficient and aesthetic incentives.

If you have an external masonry wall, which is exposed to the conditioned space of the unit, then you have very negligible insulation and a massive thermal conduit between conditioned and unconditioned spaces.You would be doing far better by your future tenants to insulate this wall than worry about loosing 2-3" of living space or the aesthetics of a brick wall.Where this is a masonry wall - first confirm if it is a single wythe or 2 (or possible 3) wythes of brick (with a air gap/drainage plane between the outer wythe and the inner).  

Finally, aesthetic improvements aside...you need a decent reserve to cover inevitable surprises that will, again inevitably, cost more than you think.

All in all I estimated the costs of repairs at $10-15k, which is an incredibly generous amount, but that would give me room for unforseen expindetures.3) A family member of mine has the same exact floor plan to the house (although the foreclosure is more aesthetically pleasing and has a nicer feel to the inside) She also lives across the street.

If everything is equal area, location, bedroom, bath, sqft then it comes down to layout and aesthetics. 

Most people think that this is only for aesthetics.