forget letters. miami is easy too. 

There is no easy answer so you'll have to decide which path will give you the least regret.  

Now all taxes are based on a super low rate you can’t fight. 

It may be easy to rectify, maybe not, depends on your jurisdiction, the issues involved and the City's stance. 

Not an easy thing, but saving 20% or more on the cost of a new home seems well worth the time and effort if you ask me.

Have proof on hand (easy enough to find) online of the missed tax payments and any documentation that supports that he specifically didn't pay his taxes.Probably a simply mistake on his part, but now if he wants to develop on it, he either has to land lease it from you or buy it back.I'm not sure how the whole tax deed thing works, so that would be something you have to figure out between the two of you.

This isn't easy to measure directly.

Commercial valuation is easy.  

A handy search bar in the upper right makes it easy to find previous discussions, blogs, podcasts, and other resources.

It very well could become a large enough investment to be worthwhile, also solving for "unexpected emergencies ", for the most part and would an easy self management situation if you were to live onsite in one of your connected townhomes.