I did it for 10 years, and these were my experiences.
Most tenants stayed a year +/-. That left 1-2 months per year empty, and there was ALWAYS work to do when they left. Even the good ones were pigs.
I had a mortgage, but could cary it if need be. I needed to carry it on the empty months, and when the tenants were late. Some were always late, all were late at some point. Several times I had people move in, and back out in a few months as they got a different job/separated/bought a house, etc.. Count on that.
If I were to do it again, I would be a lot tougher on the tenants. We have VERY tenant pro laws here, but if you follow them strictly, it's easy to win as a landlord. KNOW YOUR LOCAL LANDLORD/TENANT LAWS and exploit them . I cannot stress this enough.
At the end of the day, it wasn't a lot of work, and some of the hassle was my fault because I wasn't a big enough prick. In 10 years, I made $50k just on the mortgage side, and used it off my own home.
Mission accomplished. I then sold it.