The main challenge with some of these are the dimensions of your lot and configuring the site to allow the minimum stacking of vechicles.Depending on your use, a 5000 sq ft building may be tough to fit in this size lot when looking at how much parking you want/need, building setbacks, landscaping setbacks etc.   

Is your main goal to house-hack or are you looking to do BRRRR?  

Despite a challenging economic environment marked by inflation and slowing consumer spending, major dining chains like Taco Bell, Outback Steakhouse, and Applebee’s are pushing ahead with expansion plans.Yum Brands—parent company of Taco Bell, KFC, and Pizza Hut—opened 894 new locations globally in Q2 2024, marking a 5% increase in total units from last year.

My main critique is in the "Majority" of the cases you and others who will take out a Heloc will eventually refinance to consolidate it into one loan/mortgage.

Not my main focus. 

I'm comfortable with all of those, but I know that there is so much more than goes into your return than just those three main levers.Specifically, I'm getting hung up on 1) financing, 2) closing costs on both ends, and 3) holding costs

Turns out, heloc underwriters are trained to use the Schedule E as one of their main sources of information, more so than any leases or receipts you might include as part of your application.  

My main concern is seeing that a lot of clients are using cosigners and coborrowers to qualify for houses and are having trouble qualifying based on their own incomes.

Most of the opportunity seems to lie just outside of the big circles around the main part of the cities you mention. 

They are also simpler over the life of the unit to maintain because there are just three main components instead of four(+) with HVAC.