The very best thing to do is locate real estate investors, landlords, and rehabbers/flippers in your area. If you have a local association with any kind of event, go and talk to people. My ex had many residential properties (single-families to six-plexes) and while it was profitable, he wanted out of it within a few years because of the sheer stress of being a landlord and the fact that it didn't scale so well (the more properties he got, the less he could do himself to save money). If you're buying large buildings and can afford a caretaker, that might make it less stressful but my ex was managing a lot of smaller properties that were spread around town and could not be maintained by one tenant.
Cashflow can be stressful if you have vacancies, late payers, or evictions, but it was really the renters that were the most difficult to deal with. If you are profitable enough to hire a manager or on-call service so landlording doesn't infringe on your evenings and weekends, that will help too. Maintenance also is a lot of work. It seems like it would be a once-in-a-while thing but there are a lot of renters who are calling monthly or more for all sorts of problems, plus the groundskeeping, graffiti/vandalism, cleaning up a demolished apartment after cops raided one of your tenants for drugs (with vents ripped out of the walls and the door broken down)... which reminds me that you may want to try to specialize in rentals in good areas. All of my ex's properties were in a high-crime urban area and it was not the kind of job a lot of people would want.
So from experience, my main advice is to make sure you want to go for it and have a realistic exit strategy if you hate it or start sinking. Then get yourself an accountant, a lawyer, a buyer's agent with experience working with investors/rentals, and an insurance agent. Once you have your go-to people, all the questions you have will be answered. If you feel like you can't afford any of those professionals, I guess my advice is you probably can't afford not to have them and still do well in investment properties.
I also don't agree with the comments that real estate is "very risky" relative to many other businesses. I agree with commenters who said you don't need to form a business entity when you fist start buying rentals (my ex incorporated later but I think financing was easier when he started investing as an individual than it would have been as a new company with no other income/assets or credit).
