Edit: I stand corrected. Thanks, I understand now.
This is not a very smart way to do things. You'd be much better off getting a credit card with no fees and rewards points, buying everything with that, and then paying it off every month. You'll have stronger legal protections on your purchases, and you'll earn reward money without paying any extra. You can even pay off your bill with the reward points. And as a bonus you'll build up your credit score, which can affect you in lots of ways unrelated to loan rates.
No. Rewards are funded by merchants (interchange) and by people who actually pay the 19.9% annual interest.
But I hate it. It feels insane to me that we as citizens don't have more regulatory control over credit systems. I envy you, but I also know that what you are doing is not practical for me.
They'll likely close your account for inactivity after a few years, and the account stays on the credit report for a decade after it's closed.