Are wedding cakes typically 3" or 4" in thickness? I would like a cascading stack of hearts. But there is a horse and carriage that will leave little hoof prints and wheel marks from bottom tier up to next tier. Will that be too far for the horse to "jump"?? Or do I need to do something like a molding chocolate small bridge or something?

4"

You could carve out a road like this:
http://cakecentral.com/articles/662/how-to-carve-a-spiral-cake

I LOVE IT! Thank you!! That gives me some ideas.