One thing to note for you. 99% of real estate agents don't understand the true investor's perspective so the advice you are getting could be skewed, especially since you are new to REI. It's not just about the rents. If they haven't worked with investors, they won't know how to help you assess the rehab costs and as has been said above, rehab costs on 1900s multis can provide some surprises for you. Knob and tube wiring, asbestos, clay plumbing lines, abandoned underground oil tanks, mold. Only an agent who is an investor and works with them can help you find these unseen issues. If you don't find them your first investment will not earn you what you think when you first chart it out.
And if you are just starting out, you want to stick to a two-family to start with. You want to evaluate who is renting in the area. Is it in a good school district, one that families will rent in for the schools, or is public transportation to somewhere important as well. Being a first-time landlord is never what people think it will be so you want to limit your personal exposure by not over-buying on units to start.