To get the bullet behavior to move from right to left change the bullet angle of motion by 180 degrees. I think there is an option to not rotate the object.
I posted a simple endless runner example awhile back asking for help with the jump. You may find it useful. I just move the scenery back to the other side when it goes off one end, but I wasn't trying to make varying platforms at the time.
Making player surge towards center of window
There is another example of a vertical scroller here:
Vertical scroll platform
As for using arrays, yes, that's the usual approach, however, since you can easily destroy the objects when they get to the other side of the layout, it isn't strictly necessary. You can create a loop to generate the various pieces of the platform with random properties and set it in motion a certain distance behind the last platform.
Maybe someone has an example using arrays.