I agree that if there have been add on's to older homes specifically, but in general....there are often things done wrong.   

Stocks, bonds, social security, insurance, family estate planning, plus add on REI.  

(Some landlord insurance this is included, others are an add-on).2) Rent Guarantee Insurance (which I think you're talking about) will cover the monthly rent for a period of time if the tenant stops paying.  

I don't have the money to afford projects like an ADU or sqft add-on.

I would go back and look at your contact and see if there is anything about "by completing work, contractor certifies that all work done before them has been performed correctly" and if you do not have such a clause, I would have your lawyer add one for future contracts.

Make sure you have the reserves to add on.

I am looking to add one more property, priced between 100k-150k in 38115(38141) or 38109. 

The COO process includes notifications from DCRA to neighbors, who have a chance to object - like when you add on a deck, as well as property inspection(s).  

I can't speak to the add-on coaching as I didn't sign up for any of that.

Even if you are only able to add one property every year, that is 15 properties over 15 years.