One thing that makes it hard to write a truly risk-free bot is that if I buy one asset as part of a multi-trade arbitrage, someone else may buy other assets that I was intending to buy before me, preventing me from getting the price I wanted.

This resolves YES if by the close date, there is an option in the API to place multiple bets at once. Any collection of bets made this way must either all go through, or none go through.