Pretend your getting the hardest rain you have ever seen and imagine where the water is going.I would also keep an eye out for sewer lines and type of material.

I agree that South Florida may be a tough spot to find an acceptable duplex house hack, but it is possible.

Look at the pictures to evaluate the quality of the materials and workmanship of the comparable sales and align your ARV accordingly. 

I know STR's are tough due to the tourist license's being heavily controlled/shut down in Barcelona.  

From what I have heard, primarily through these forums, it can be tough to do just about anything yourself. 

In CA (my market) the seller is required to make honest disclosure statement and you can collect for material non-disclosure.I suspect you already have learned that you need to check the status of all permits. 

It's always better to check with your brother's CPA since he has all the background, but I would say short-term rental with material participation requirements met by your brother, then do cost segregation.

Also, you can't know how the cost of materials could fluctuate over your project time, so consider purchasing any materials upfront so you can stick to your budget. 

This is tough to do with today's high prices and mortgage rates, which is why so many investors have slowed down or stopped investing until the market turns favorable again.Below is an example of a single-family home in Allentown.

Given that your current place is fully covered by rent, moving to a new property where you would have to cover $400-450 more per month could be tough, especially in today’s high-rate environment.