It is hard to guess without seeing the issue, but by a wide margin the best stain blocker is shellac based Zinsser BIN.   

South Philadelphia's base zoning districts are not very accommodating either.

im based out of Fort Lauderdale but I help a few clients in the West Palm Beach area.

The first people that lose their money in a downturn are those that are lending at insanely high LTVs without adequate underwriting experience including determining if the borrower's qualifications based on credit/character, capacity, and collateral.  

You won’t end up in tax court but if you do, you would win based on everything you cited about material participation as long as you have a time and activity log that shows your tasks and provide a guest list that shows the number of nights your guests stay (easily found on the various platforms). 

We have a small fund based out of florida.

I expect if the stock market truly crashed long term the government would bail out 401Ks before STR investors based on the government's previous actions.

Of course we can't predict the future but based on everything happening it seems we will have at least as good appreciation as the rest of the country and possibly more than average.

Instead, a lender will want to see that the property currently brings in (or has the potential to based on market rents) enough to cover the monthly principal, interest, taxes, insurance and HOA (if applicable).

Try asset based lending, portfolio loans, where all they care about is the property.