Using the PERSIST behaviour for any object will make it "remember" where it was when you left the layout and then returned later.
As far as placing objects randomly, just set X coordinate and Y coordinate to;
->Create object at
X = random(layoutwidth)
This is obviously a very basic example of random placement, but you should get the idea. That code would create the object anywhere on the layout based on it's size. You could use specific numbers if you wanted the objects to appear in a localised spot (maybe only on one side of the layout, or perhaps outside the layout?)