I'm looking to add a 3rd bedroom and/or a separate apartment in the garage of one of our rentals, but I'm nervous to talk to the city without advice. 

Not able to house-hack as I have a home that I will be securing a HELOC from and looking to invest locally (including Union City, NJ area). 

You mentioned that you stick to investing in cities and avoiding rural areas, would you consider the Dover/Somersworth/Rochester areas possibilities?

I did a few searches on BP, but didn't see this specific topic, so I thought I'd give it a try.In this world of big data and the "interwebs" I am curious of anyone knows of a search that can list all-- say 20+ unit apartment buildings that exist in a city, or region. 

The one I use for demographics is called "city-data.com".

ER was not my target area, The city of Rochester was but I liked the area and the house better than the current ones available in the City.

Not sure what you are trying to get at there...Taxes are determined by the county/city. 

Need realtor for investment properties around Kansas city area.

One CAN figure out approximately how much a property sold for even if it's not listed in the records:  extrapolate the transfer taxes (state/county/city) and multiply out.Just an aside:  I remember back in the day when the appraisals were coming in short in an appreciating market (something like we have today) we would ask the buyer to pay MORE money for the transfer taxes (no law about not paying more taxes) and it would help show a higher "sales" price and help 'push' up the comps--not recommending you do that now--much more data available for all eyes.But I would recommend that you buddy up with a like-minded realtor, and work out a mutually beneficial arrangement so you can get the info you need, and they can get listings, sales, referrals, etc, that they need.Better yet, get licensed yourself and get to know the business from the inside out!

From my limited understanding of the city Albuquerque is a street to street call on quality of the area.