I really love my rentals, and I am acquiring three more this year, but I am the first to admit that I am learning all the time and my ability to choose better properties, make them cash flow more, and feel less stress as I acquire them is always evolving. I often fantasize about what I would do with a large windfall, and imagine plowing it all in to rentals at once and calling it quits then and there.
That's when I take a deep breath and realize that the best thing for me (and I believe any other new landlord or real estate investor) is to start by acquiring only as fast as you can digest the properties and make them operational and relatively problem free. To start with, I think that means one at a time. Buy, rehab, get renters in, be sure they are paying for a few months. Then buy another. Then maybe buy one or two more.
Just my two cents, but I think a slow approach acknowledging lack of personal knowledge will yield best financial results.