ZickZack

I think that interest is added, specifically you pay https://www.irs.gov/payments/quarterly-interest-rates based on the quarters you were missing taxes.
Not sure if the numbers quoted here include that already

No, it’s built into the protocol: think of it like as if every http request forces you to attach some tiny additional box containing the solution to a math puzzle.

The twist is that you want the math puzzle to be easy to create and verify, but hard to compute. The harder the puzzle you solve, the more you get prioritized by the service that sent you the puzzle.

If your puzzle is cheaper to create than hosting your service is, then it’s much harder to ddos you since attackers get stuck at the puzzle, rather than getting to your expensive service