I'm very late to the conversation here because I'm just now thinking of adding an ADU and doing due diligence.

Its certainly doable with the right due diligence.

In your due diligence, if any leases are coming for renewal you should ask for them to be delivered vacant or transferred to month to month.

Be creative and always do your due diligence. 

Having said that i read in the long distance real estate investing book that It’s not uncommon to make an offer without seeing the property, and then doing the inspection and other due diligence.

I’m okay with spending time finding a manager and doing the random tasks that turnkey companies overcharge for, but I don’t want to spend dozens of hours trying to buy below retail.Basically, I want to pick a new-ish construction house off of the MLS, negotiate to roughly retail price, do the due diligence, get a managing company, and get on with my life.

Tiny houses can be a bit complicated and sit in a weird grey area in between illegal and legal currently (depending on where you're putting it, but it seems like you've done your due diligence and research.  

Eventually you will have the ones you never saw coming and see there true colors once they become comfortable or when it’s fine for you to even ask them nicely to move.Basically, Always have the upper hand once you lose that, you lose all respect and control, you lose that great tenant with the so called great credit score, leases are imperative and have to be very diligently written and spelt out to a T!

I thought I did all of my due diligence on selecting the right one now I’m not too sure.The unit is newly renovated as I was living there for the first year of ownership and did a lot of work to make it turned key (I guess).

To do this you will need four things: 1) a strong test ad in due diligence to prove that the demand is there 2) a dealer's license and an agreement to participate in the 21st Morgage's CASH program 3) the capital to make the necessary renovations to sell the home and 4) the knowledge and the ability to advertise, show and sell homes.There's no reason to fear the occasional loss of existing residents as long as you are prepared to replace them.