The main house is split into 4 units, and the fifth unit is a carriage house (on top of the garage).

So now you have a former carpenter evanluate an electric system or an former electrician evaluate a cracked carriage beam... - sometimes almost comical, if it would not be so serious.A great inspector is professionally trained in this field (not as a contractors), uses software and has a systematic approach to evaluate a home, identifies all problems correctly, but can also explain the real world consequences and not refer for everything to "further evaluation by a qualified contractor".

-- then buy a home with a basement apartment or carriage house and rent that out. 

I would double down on your local market and expand your search for single family homes with carriage houses.

(Sorry Huntsville.)Find a home with a basement apartment or carriage house and Airbnb the heck out of it.

Property overview;3 bed/3 bath/3000 sq ft fully renovated house4 car garage that has a carriage house above that could be a ‘getting ready’/bridal suitePavilion with commercial kitchen, electricity, bar area Pond and grassy area for ceremoniesParking area for 100+ carsRustic barn that could be updated for additional event space. 13 acresI have experience running large scale, high end events and would like to take on an operational/boots on the ground role with this property.

(Either 5% conventional or 3.5% FHA.)You can do a live-in house hack if you wanted...either rent-by-the-room for the rooms you're not using or find a nice place with a basement apartment or carriage house so that you maintain some privacy but still have an income suite to generate revenue.

What I'm in the weeds with/end goal is to accurately determine the 'space' available on a parcel for an ADU or carriage house.

I have a lot of clients who want to house hack in Denver with a carriage house or basement apartment.

Don't put the horse before the carriage.