I calculated a $30k profit. 

Deduct NEW property taxes after you buyDeduct home insurance costsDeduct maintenance percentage, typically 10%Deduct vacancy+tenant nonperformance percentage(we recommend 5% for Class A, 10% Class B, 20% Class C, good luck with Class D)Deduct whatever dollar/percentage of cashflow you wantNow, what you have left over is the amount for debt service.Enter it into a mortgage calculator, with current interest rate for an investment property, to determine your maximum mortgage amount.Divide the mortgage amount by either 75% or 80%, depending on the required down payment percentage - this is your tentative price to offer.If the property needs repairs, you'll want to deduct 110%-120% of the estimated repairs from this amount.Be sure to also research the ARV and make sure it's 10-20% higher than your tentative purchase price.As long as the ARV checks out, this is the purchase price to offer.It is probably significantly below the asking price.

I have experience using DSCR loans that calculate the STR revenue to purchase smaller single family homes.

Here's a bit more in detail about how rates are calculated for DSCR loans:1.

They take your electricity bill for the year and do a straight line calculation which is almost always wrong because your electrical company charges vary by the hour, and solar production vary by the hour / season etc.

Understand the fees involved and calculate the total cost for an entire year of management so you can compare the different managers.

Just be sure the calculate in the interest you are paying on that HELOC into the new project.As for banks, my experience has been that many banks do not like to do HELOCs on rentals unless you have a decent portfolio which they then look at as a business instead of a single rental property.

My opinion is that if people were making reasonable business calculations, these types of cases wouldn't even get there as the end result would be a judge having his eyes effectively glazed over and losing confidence in the efficacy of the sub metering solution. 

When analyzing a new build/“build to rent” property as a rental, what percentages/amounts are others using for:-Maintenance/Repairs-Vacancy-CapexI’d assume it’s less than than existing homes, but by half or is it safe...

Obviously not really big deal if he owns it out right, but it will be something you want to consider in your calculations.