Congratulations on jumping into the STR market. 

I am in the Milwaukee market and we deal with this often.

I want to be able to find potential markets/listings nationally based on the return.

Are there better markets or hybrid approaches I should consider (e.g., smaller multifamily properties that accept Section 8 tenants)?

My duplexes already at market rent and only exsecting 3% raises each year.

Louis market:•How strong is the demand for Section 8 housing in the area?

Lexington is a weird market with low occupancy, 90-92%, and there aren't many assets in the market.

Sure, mortgage insurance eats into your cash flow a little bit if you're putting less than 20% down but in the scheme of things it's really not that much.Also, you won't have 20% equity in your property in a year assuming you put 10% down unless you are forcing appreciation or you somehow get some high market appreciation.

My primary focus is on properties in Miami and the surrounding areas, including Homestead, as I’m familiar with the market here.

I also wouldnt let your mom go into 2nd position on an investment property with any sort of restructuring; it doenst sound like she's in a position to risk being wiped out.Overall, though, if you want cashflow on the new property but cant achieve that after a refi into a market rate loan, it probably makes more sense to just flip it, pay off your heloc and your mom, and use the remaining capital for the next deal.