Square footage is usually listed based on tax records or appraiser measurements. 

Get a smaller apartment, sell stuff that you dont need.It takes some drastic measures to leap forward.

Also, it should be fairly easy to determine the square footage by measuring the length and width of the ADU and multiplying them. 

It’s not accurate to use median household income to measure affordability.

I also purchased a laser tape measure so I can verify bedroom and other measurements quickly. 

Again, that sounds great measuring it using that worthless number with a % behind. 

I  used Home Depot's Web site to select the doors I wanted and also used the Homewyse website to get a second set of numbers, and they came both pretty close to each other at $1800 products and $1300 labor.I then contact Home Depot to get a person on site to inspect and take measurements, and a couple days later I get an estimate with two sections: Customer Pickup #1 for $2695, and Installation #1 with $0 total.

Questions, or measurables that I can quantify, are things like:i) cost per square footageii) no. bedroomsiii) distance from public transportWhat are other measurables around property purchases?

I would say effective age of the property might be a better measure.

If renting, what other measures would you do to ensure your property is protected (yearly inspections?)