Design the artwork pieces you want in the timeline in Photoshop ot Illustrator. Import them into AE. Add the first one to a comp. Parent it to a null. Add the next one. Put it where it's supposed to be, and parent it to the null, If you run out of room, move the null horizontally until you have room. Repeat the process. When cone, animate the null horizontally.
And if this stuff sounds like Greek, go here:
So I have to create the timeline manually? Isn't there a way to put it in motion tile and say "each copy, increase value by 1"?
Well, you could make the comp containing your timeline wider than the composition it's being used in and use expressions on some of the numbers inside it so that, once the Motion Tile in the main comp moves a certain amount, the number counts up by a certain amount. This would make the number jump up before it comes on screen in the main comp. If you need the timeline to be really, really long, this may be worth the effort involved.
Alternatively, you could create an expression on a numbers effect (or a text layer Source parameter for that matter) that ties into the layer's layer index, duplicate the layer as many times as you need for numbers, then spread one of them waaaaaaaaay far over to the side and use the distribute function in the Align panel. Of course, you would need to be sure that the layer index doesn't change as you add to the project...