From what I've gathered the properties will not begin to cash flow significantly better, you are in a market that cannot easily absorb unexpected capital expenditures (greater risk to you in the future) and the principal paydown is pretty meaningless for a while.

. $30k can turn into $8k or 0 really fast - whether that is due to unexpected costs - especially on an 1875 vintage home - or your ARV estimate being off.

What are some unexpected challenges you've faced?

Florida is really competitive with short-term rentals and I've heard many stories of people diving into the market over the past few years only to find it difficult to cash flow with unexpected costs, rising interest and insurance rates, higher price points. 

It's going to be a steep learning curve: there are always budget and timeline overruns, unexpected costs, etc. and that hard money loan will kill you every time. 

These expenses can include property acquisitions, development costs, or unexpected repairs.

As for the cheaper markets, I would look to do mid term rentals in the Rust Belt near hospitals like the Cleveland clinic to maximize the income to help mitigate the downsides and unexpected expenses associated with those markets.

Moreover, during the inspection process, we discovered an unexpected basement space, adding further value to the property.How did you finance this deal?

unexpectedly, my ex-STR that did not get an STR permit when quotas were enacted, I got notice is getting its STR permit.  

If, while running your numbers, the returns are within range to your criteria, do not lower the expenses to "make it work", but just know that some months may be higher, some may be lower, and if you have the cash reserves to support a higher bill or unexpected repair, then the underwriting at least helps you mentally prepare ahead of time.Any calculator, based on the inputs from any noobie or seasoned professional, will NEVER be the same as your actual numbers.