A 420a Sure looks like that would be allowed.

A 420b For Spinning Throw, first you use your ki throw, then you resolve your bull rush. So again, I'd say that when you piece it all together you can indeed place your target in a dangerous square, and then can - if you choose - bull rush the target out of that square.

A 420c You don't need to be adjacent, but you do need to threaten. Otherwise, you'll be unable to make the trip combat maneuver necessary to get the whole chain started.