and I'm gearing up to start the rehab soon.I invest remotely but will be visiting Detroit in a few weeks to spend some time on the ground.

You should engage a property manager though for this property and if you think there are grounds for eviction I'd try to move on those with an attorney ASAP.

Not only is the demands of each buyer going to vary by market and submarket, but also asset by asset.My favorite example of this was an old season of Flip or Flip, where they bought a house in LA county, versus their standard stomping grounds of Orange County.  

Give him a call, apologize for asking him to put TP in the trash can (that will create common ground and a more reasonable starting point for a resolution), let him know that prior residents did not have issues, have his family curtesy flush, and let him know that future clogs are his responsibility. 

And our company are state licensed real estate broker and general contractor with boots on the ground, actual data from our own operations (we operate above 95% percentile).

It is unfortunately not made out of reinforced poured concrete and instead stone and mortar that could become loose from too much ground movement.

We don't do an 80/20 or 70/30 rule as it doesn't give you any ground to stand on if ever audited. 

Having been in many aspects of real estate throughout my career my favorites are ground up construction and note investing. right now note investing takes the cake as it can be done in any environment whereas ground up right now is very challenging. 

The interior and grounds need a major renovation, which I am estimating at around 1MIL.

They help the investor also connect with a PM on the ground and potentially contractors, which can be useful.