For more planets change the "every tick" to "for each planet" and add another "every tick" event below and move the "set position" action to that.
To make it work with the bullet behavior you'll have to covert the speed and angle of motion to vx and vy in an "every tick" before the events and back at the end of the events. Also the "set position" can be removed and the overlap and bounce event should be either before or after the events.
Here are the conversion formulas:
Vx=speed*cos(angle of motion)
Vy=speed*sin(angle of motion)
Angle of motion=angle(0,0,vx,vy)