I recommend you do this each year to adjust for utility increases and other variables.

In a soft market we are simply experience a much higher percentage of unqualified tenants.

I am wanting to identify raw land parcels in my area with certain criteria that I can prioritize based on specific variables.

I operate this condo as AirBNB rental and retain a percentage of gross income for my management services each month.

Each of these variables will dramatically change the advice I give the individual asking me this question.

He deposits money into all four every month from the rent checks he gets at the percentages that have so far worked for him.  

Lets face it real estate investing has many moving parts and many seen and unseen variables that we as investors must navigate all at the same time. 

Depending on wind, air leakage, insulation levels, etc you can have some variability in actual temps.

But for a BRRRR, should that percentage be calculated based on the ARV of the property, my all-in cost, or should it be based on how much I pull out of it in the cash out refinance?

You have to hold back a percentage of money in case a late claim comes in.So, for you, the first step is to get a title report and see what it says, then to get the mother appointed as executrix (takes time & money and her cooperation) but then during the process and after that you never know what she is going to do.