The property tax savings are going to be in the ball park of 40-60%, but to be safe you should double your expected repairs budget when calculating the NOI.If you have any other questions, or want a more in-depth response, I would love to help!

I believe that is safe to say for most markets in the US regarding either SFH or MF.

I hope you are staying safe in this difficult time. 

Goal would be to acquire 20 rentals by the age of retirement, with some already starting to be paid off.I am in the same boat as you, and I focus on safe appreciation all day (small cash flow for safety and then focused on markets on that appreciate). 

I'm assuming that this situation wouldn't pass inspection, but one could argue that all the spaces the guests have access to (i.e. bedroom, bathroom) are safe and habitable + the guests wouldn't be exposed to the kitchen.Also, do the city inspectors inspect other parts of the home the guests won't access (i.e. inspectors check the basement for water infiltration even though no guests would ever be living or even going down there). 

Make sure they feel heard and assure them you will do in your power what you can do to make sure they are safe.

Detroit/Flint are gives great return in good neighbourhoods if one has the right team on the ground, More then willing to share why we are investing there and how we do it safely

Quote from @Matthew Becker: Ask off as much as you need to be safe. 

You may be safe to get non-commercial F/F adding up to 2 ADUs to a duplex even though by rule this does not qualify (in my area I have never heard of this being an issue). 

Since it was a structural change, you need an architect or engineer to draw up plans that make sure the new changes are safe of course.