What is the top speed?

Top speed depends on the rider and the paddle board, but generally top speed is 5.8mph.

What happens if I fall?

The Prop comes with a kill switch that you can put your leash through . When you fall the kill switch is pulled off and the motor will immediately shut off.

how does the battery stay dry?

The battery is in a waterproof box.

How does it attach to the paddle board?

Window latches!