It will map out the rooms and give you dimensions including square footage.

The previous owner added some square footage to the house without a permit.

What's the value difference between 3 and 4 bedrooms w the same sq footage. 

ARV would probably put the sale around $450-500 depending on a few factors (can any of the basement be finished out to make more sq footage etc).

Most experienced investors can offer sight unseen with 0 day inspection period by knowing the year of the house, square footage and if there has been any repairs done recently to the property.

While the bookkeeping will likely be complicated, is the accounting/taxation on this STR based on 100% STR income/expenses allocated 100% to business and general house expenses (mortgage, utilities, depreciation etc) pro rated between STR/personal residence based on sq footage?  

I can't tell you how many properties have units easily convertible from 1 bedroom to 2 bedroom units, units with favorable dimensional standards which can boost rents with no photos to showcase these attributes, assessment square footage that is not correct,  upgrades not identified in the marketing materials etc.

Your "in between" on your pricing and your square footage. 

That type of square footage is probably like a $250-325k rehab budget.  

People who know the values of the properties street by street, They can show you that in the last 6 months there are have 4 sales for a 3/2 in similar square footage.