I've created a layers template with 5 layers which I will be using on 160 different lease plans. How do I copy the template onto each LP to avoid recreating each layer from scratch?
You could just save as an Illustrator template (.AIT) file, and use the template to create each new file. This is probably the easiest way to do what you want, though it's hard to say without knowing more about your workflow.
If each of your files is already made and you don't want to make each into a new file, you can copy and paste the contents of your template file into each one. In the layers panel, in the options drop down menu, check the option called Paste Remembers Layers. Then just select all, copy and paste (you'll probably want to paste in place). This will preserve any layers that contain objects that you've selected. If you need to create empty layers, you could make some dummy objects on them that either aren't in the way or that you can delete after pasting, to make sure all of the layers are copied correctly.