The only variable is the mortgage and a $10k swing in either direction doesn't seem to move the numbers much.

There are a ton of variables to developing a property.You need to check if buyers will purchase the land un-entitled or will only buy with zoning in place.

With this same property and an estimated rent at $1000 a month here are the numbers:Mortgage $485 (75k at 4.75 for 20 year amortization)Taxes $100 (This is a guess because I have no idea what they would be in your properties area)Insurance $50 (This is also a guess but I am basing it off of my own rentals)Property management at 10% $100 (This depends on if you will be managing it yourself or not)Capital expenses savings for repairs 10% $100Vacancy 10% $100Monthly cash flow = $65 (6% APR rate of return on your 13k left in the property).Now there are several variables in this example.  

There are tons of threads on here about entity types- but ultimately there are SO MANY variables that there isn't really a good blanket answer. 

Long-term mortgages tend to be quite variable when it comes to hard money lenders.

Confirm with a good CPA, obviously, but it's another variable in our equation that we can use to our advantage.

And what are the variables that need to be present to fall under the rules for commercial valuation?

If you don't already, you need to have a spreadsheet where you can quickly plug all those variables in and have a good idea of your potential ROI. 

Way too many variables involved each roof, quality, labor, warranty is difference.....

There are so many variables that could completely change your numbers.