Where to find data on a neighborhood?

[Account Closed]

I hope to be purchasing a small (3-unit) multifamily in Brooklyn this spring hear a lot about researching an area before a purchase, but I'm unsure where to find the information I need - and how to be sure it's accurate and complete when I find it. Places like Zillow and Redfin seems to often have contradictory info for sales, foreclosures, average rents, and charts of real estate values over the years.

My buyer's broker has given me some stuff - mostly recent sales and current inventory - but this doesn't go deep enough for me. For example, is there a way to find out (roughly) how many units are for rent in a neighborhood, so I can see how saturated the market is? And how important is that, when I only need to rent out two units? I feel like it isn't - but this is my first time, so I don't know what I don't know - and that always terrifies me.