The current area we are living in is very expensive (Boerne, TX) and is a heavily deed restricted region.

What a great town.Check out - https://www.cityhs.net/1265/Short-term-Rental-InformationShould have some rules and regs for you to peruse.I will say that lakefront is often restricted or banned for STRs there.

My main concern is that someone  told me that there are HOAs whose rules are so restrictive that people who bought lots found they couldn't even build.

You want a ratio of 1 to 1, anything higher is more restrictive and can mean you will get less money then you are after. 3.

I verified with the city and investors can add them with meters on single-family homes as long as there are no deed restrictions.

Because two thirds of the buyers are Mexicans, who were much less affected by travel and other restrictions.

Also depending on if you want to stay in Clearwater or not there are also some local restrictions on STR.

As the property is a SFH (Single Family Home) it is exempt from the most restrictive rent control measures in place. 

And there are strict loan covenants  that require doing on going work with Naca  deed restrictions on when you can sell etc etc. 

They have restrictions in place that place limits on days per year, occupancy, etc- but it's still doable (& profitable).