You know a similar thing happened in Kansas City (more specifically Jackson County, MO) regarding property taxes in 2023.

Similarly, if you put several Class D tenants in a Class A 4-plex, what do you think will happen to the property?

Where is the property located.assuming the seller added the ADU and did not disclose the ADU in disclosure forms, you may have recourse (depending on the rules of your jurisdiction) but it may cost you some legal fees. 

I would do some online research into Realtors in your area to see if you can make a connection.As @Michael Dumler pointed out, wholesalers are going to be a more reliable source for consistent off-market properties with margin.

I'm a licensed contractor in NYC and I have a good friend who's family owns a property here in Crown Heights Brooklyn that’s basically all paid off and taxes are up to date.

Since acquiring a four-unit property on the Northwest side, my bi-monthly bill has typically been around $500.

I was wondering what your experience has been, good or bad with buying rental property in close proximity to the firehouse/station?

Your lender should use the f/f that can finance the property.  

I just think for me $15000 would have been better spent on a down payment on a property.

We have a mixed use apartment/commercial property for sale where the owner would entertain seller financing.