If you own seven apartments with an average rent of $1k, your yearly revenue (not profit!) is $84,000. That's microscopic by any reasonable standard of company size.
The average rent in whatever is somewhere around 50% of the income, so if you own 3, you don't need to work.
So, rental income from 3 houses = 1.5x
Even if we assumed that all three homes were owned outright, you'd be on the hook for property taxes, maintenance, and utilities for each house. About half of my monthly expense minus mortgage is on these three line items.
Therefore, 1/2 of 1.5x goes straight to property taxes, maint, utilities leaving your income at 0.75x. You have to pay your own rent/expenses out of this.
Living off renting isn't foolproof at the levels you suggested.
I don't know if you said "houses" on purpose. Houses are going for more than 0.5 income.
Can be a 4th property. Can be that 1 of the rental is simply an independent floor in their 4 stories house.
Either way, if you own at least 3 properties you can have enough income to live.