Scrolling Background?

Hello. I am trying to make an old school style top view shooter (like 1942, ikaruga, etc.) and I was wondering how to make the background look like it is scrolling. I was thinking of have a rectangle empty object, positioned where the top of the screen would be, and then I would have it randomly spawn some objects at a set velocity.

How would I do that (as in, instantiating an object selected from a few types, from anywhere within a certain x axis, at random intervals between 5-10 seconds)? Thanks

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