I own two rentals, and hope to get 3-4 more over the next few years. There is a TON of up-front work to getting a rental business set up the right way, but after you get the properties in place...it's manageable.
Up-front work includes things like setting up an LLC, attorney's fees, hiring a CPA, learning the lingo, reading the landlord statutes, reading about legal disclosures such as discrimination laws, lead-based paint disclosures, etc, getting set up to check applicants' credit reports, buying filing cabinets and developing a filing system, getting a PO box, getting a 2nd phone line or "distinctive ring", joining landlord associations, lining up a good set of contractors for repairs, learning about radon, and the list goes on and on.
I have a "high quality subsystems" approach to my properties...so I spend the money on things that it would be difficult (although not impossible) for the tenant to break...such as going from 1950s era cloth wiring that's ungrounded with fuses to a breaker box and modern grounded romex wiring and fixtures. Smoke alarm systems (yes, they can remove the batteries, but by code our area requires that they be house powered with battery backup). Changing plumbing from leaky cast iron drain pipes to modern PVC. Solid roofs that don't leak, with shingles that have UV-limiting coatings on the shingles. Guttering/draining systems that move water away from the foundation so you don't get foundation settling and cracking porches/driveways....and so on.
Don't spend lots of money on flooring, countertops, cabinets, trim carpentry, etc...that's the stuff they can tear up.
So basically, I buy a house, spend an enormous amount of money on the systems, a little on the appearance, and rent it. The upside is that I've only had one maintenance call in 2 years between the two properties...and that was a 30 minute fix.
Most landlords tell me I spend too much...they leave the old leaky pipes, charred wires, and leaky roofs...and deal with the repairs as they occur....every week according to their own accounts. I prefer to do it differently.