Lesson #1: Do not believe those ads!
You will not sit home and collect rent from your tenants. It will not be Passive Income, nor will it run itself.
A building looks solid, but it's really a mystic being, undulating with wants and needs. It will need maintenance, painting, garbage removal, lawn cutting, snow shoveling. It will cry through its plumbing, get chills through its heating system, have fevers through its air-conditioning system. And, like a spurned lover, will often have late-night tirades.
You will be called about all of it.
You will often be a babysitter, referee, detective, and psychologist.
You will need to be an appraiser, handyman, bookeeper.
If you do all this well, you may make money.
It's a business. Better to know this ahead of time.