My interest, as a newbie, is to find properties that will give me a healthy rental income and as I earn enough from one to keep adding units.

So, given that there was a crash 10 years ago (and some people forecast another big one soon) and there are plenty of investors that do ultimately fail in healthy economic times, what does that look like, and how do you recover?

It's in your best interest to keep a healthy reserve balance for the property to support these ebbs and flows of cash flows.

If you wanted to buy a lot that does not have existing BOHA and were able to get as many tests as possible done ahead of purchasing (perc test, soil test, engineering, surveyor, talking to town building dept. etc.) and they all came back ok I'm wondering if anyone has ever heard of still ending up with an unbuildable lot somehow.  

Do you also have a healthy savings account?

with a healthy cash position. 

If you decide you are more passive oriented then my BP article from last year might be helpful Three Key Routes for Passive Real Estate InvestingIf you are looking to own cash flowing rentals in economically healthy markets then best options are generally in the midwest, and some in the southeast.All best in your REI!

Do they look healthy? 

It still seemed healthy to me and after this tax year, business profit has been very well.

Without knowing your original investment or cost of improvements to look at the cash-on-cash return, it sounds like your ARV and net profit are healthy.