You're not worried about monthly interest payments, loan origination fees, etc. 

Add to that the original $100k that was borrowed, the total received over 15 years should be $205,000.

Our background is primarily in software, which we hope to use originate differentiated, high-quality deals.

We originally hoped to rent as a mid term rental in a smaller town with a hospital, but the market quickly became oversaturated for the small demand so we decided to shift to long term rentals on both sides.

I was originally looking at Indian rocks beach but have extended my search to Seminole (both zoned for STR).

If so does the cash out reset the loan to the original amount or does it increase it to include the value of the new unit (i.e. original loan was 300k and after cash out it becomes 550k?)

Originally listed for $149k.

Searched four sites and came up with a different decision than your original decision to go with them. 

It’s been unable to sell because the original house was a single wide in the 70s that was then added on to.This makes financing either difficult or very expensive for people (especially since it’s a low price point and mainly first time buyers).We would be paying cash - so it’s not an issue for us.

Has new flooring and appliances but kitchen and baths are original but well maintained in above average condition.