If you are good at spreadsheets, you should be able to create tab in the sheet that lists all expenses with a “class” column, and then sum all transactions per class in the aggregate tab using formulas with it statements.  

Having the money to buy and not understanding the business, in depth, is not a good formula.

Thinking, if regular formula we use (0.75*ARV-Rehab costs) is good enough to deal with it, with higher risks/ unknowns involved... should I re-negotiate or back out???

In our land valuation process, would you recommend maximizing our land usage using the SSA formula?

For labor, I did a mix of Google Searches for what I might expect to pay and asking a contractor that I worked with earlier on a small project.Everything is done with formulas, so I can just enter in the number of units to calculate a total price. 

Formula is:  (Pessimistic + 4X(Most Likely) + Optimistic)/6

I also agree with @Chris Tracy 's general "5 steps formula".

In theory, OPA should've come up with some kind of formula to accurately value the underlying land.

Brian Page has some formula for this.

HUD has a formula they use to determine affordability and it will come out different for each applicant.