My question is if I made the HELOC go away from my cash reserves, could we then agree to seller finance the remainder and then use the cashflow from the STR to pay her plus give her a percentage to manage the property? 

I also don’t have a percentage, but in general - I have found Facebook Marketplace to have the “coldest” leads.

Look for a market where a higher percentage of the population rents than national average.

Typically it's meaningless until it goes hard and percentages of pp have definitely dropped over the years. 

They say by 2028 the percentage will be closer to 30-40% of people. based on those numbers 500k plus 3 mil plus I suspect less than 2% of all folks in the US would qualify and maybe less than 1%.. 

It is important to note that my business partner is a family member and we are aligned on pursuing whatever strategy is most optimal for our main goal of acquiring as many properties as possible collectively, regardless of ownership percentages on paper. 

Expressed, in percentage terms, you'll need to put a lot of zeros after the comma to get to the first figure.

Only a very, very small percentage ever make decent income.

The BP calculator uses a percentage for both cap ex and maintenance.  

If the property is in a rough part and only rents for 1000 and is harder to manage than a rental that's double that and it's percentage based they gave to be compensated fir the extra work.