You do have to have as many ROADS sheets as you do tiers, and then one more to try and blend any joins... unless you hide the join with a bridge or a tree.

I think you are doing well with the contouring. It does take some time and patience to get it right. Roads are a tricky one. I did a city a long time ago and cheated a little bit by using 6 or 7 tiers a bit like a disorganised wedding cake. That way each tier cast a shadow where necessary over the roads and houses on the tiers below.

They only really work at the default scale of 1.

You can use them at other scales, but not as a connecting symbol. To do that you would need to right click on the map while you have the symbol on your crosshair, and set the bottom two checkboxes like this, then paste them individually.

It's looking really good already. If you want a few more tips about using the cliffs, Ralf did a live mapping session on them here.

It's fine to use the assets designed for use with CC3. That's why we make them.

Equally, it's also nice to see people having a go at their own sometimes. I think you've done a fair job :)