Have you planned your investments for retirement? Let us say - yes, I am going to own 13 houses, and I will live off the rent. I will also have a Roth (whatever that is - I'm Australian)
If yes, what income will you get from taxable investments, and from untaxable investments - $20k a year from my rent, $10k a year from my Roth
Now, I assume that a Roth doesn't get taxed, and your rent does, so you will have to pay tax on your $20k - what is the US marginal rate for that?