Random Items Rising From the Ground (aka Off Screen)

I've seen an example or 2 but not quite what I am looking for on this. I am trying to give the illusion of falling down a hole for a bonus level, and you have to control the falling character to go around objects and pick up items (think of Dead Pixel if anyone remembers that game from a year ago). I want the level to go endlessly, or at least until conditions are met.

I want platforms and items to random spawn from off screen at the bottom and then move to the top where they will be destroyed when they exit the play area. The player will be moving only left and right as they "fall" towards the objects. This way the level can appears to be scrolling infinitely. But lets say I have 4 powers up and 3 different "collision" objects. How can I randomly choose one (or more) of the 7 items to spawn at the bottom off screen in various positions along the X axis, and then move them upwards (I assume I use a path for the movement). Eventually I will deal with timers and randomizing the % of the time a good object appears versus a bad one but right now I just want to get an example of randomizing the item and spawn point.

Cheers!

This is so far a great start, thank you. Would you be able to point me in the direction of something that might help more with the randomization. For instance, I got this to work by setting 3 individual items to randomly spawn and "fall" up every 3 seconds. But I would also like to randomize the items that are created and also the time between the object creation (which I assume I can just randomize the time within a range too, it's the random objects that confuse me). Sparckman's tutorial is randomizing 1 item exactly every 1 second which works in his application but mine is a little more complex than that.