As someone that owns rentals, I would advise you not to invest in rentals for "passive" income. Rental properties are a business, and like any business, they require your skills and your time. If you want to do this, make sure you understand the math of successful rentals and what is involved in managing them.
Agreed. We, however, priced a hired property management company into our rent structure. Once we have a property ready to rent we spend very little time on it - that's what the property management company is for.
The process for a rent-ready unit has proven to be almost completely passive. We have four rent-ready properties that all together net us a bit less than $20,000 a year. I'll take $5,000 an hour for 4 hours of my time a year.
We buy properties cheap because they need some work and the sellers can't or won't do it. Getting a property ready to rent is a very active task because we do most of the work ourselves. Other people do it differently and limit their "active" role to the finding and purchasing of rent-ready units.
I cannot agree too much with the recommendation to actually LEARN how to calculate the various financial measures on whether a property is a good investment or not. Lots of people are too lazy to do that and lose a lot of money.