He built all the houses himself, maintains them (including the gardens) with a small team of staff, and has 1% vacancy rate. 

I have a few certificates on vacant/abandoned houses and as soon as I start maintaining the grass I start getting calls requesting to buy the property.

The first pillar is avoiding unnecessary and risky activities (don't drink and drive, insurance generally won’t cover your poor decisions) and take good care of your investments(maintain your property, etc) - these simple steps will help you prevent lawsuits before they even occur.

I have a good friend who's son has worked for 13 years installing and maintaining car washes.

My concern is location - is this too far to draw clients and maintain occupancy/bookings??

They still must maintain the budget they set.Your only lifeline may be to figure out if your state laws address this situation.

I did the math and based on the quotes if I buy i make my money back in ~6 years.This assumes no maintenance costs though since if purchased i would need to maintain it myself, vs rental comes with maintenance included.For things like AC / Water Heater / Furnace / ...is it better to buy or rent?

I also don't trust the lower end condo stock down here, ($450,00 and under) as I've worked for an architect involved in rehabilitating these under maintained properties and most seem as though they are old stick built buildings about to fall apart.

The neighborhood is rough right now due to some vacancies, a couple of condemned buildings, and a private road “maintained” by the owners of the neighborhoodAdding value to this deal won’t come from improving the property, but from working with property owners in the development to either fix up the houses and the roads or buy the rundown houses What was the outcome?

This only works if that neighborhood has a strong history of maintaining its appreciation.