@Huge85 

If you run your Deco mesh in Access Point mode, it does not matter. If you run your Deco mesh in its default Router mode, it does matter if you want your wired Satellite Deco use Ethernet backhaul instead of wireless backhaul. See https://www.tp-link.com/us/support/faq/1794/

Obviously, Main Deco must be wired, you can't have it wirelessly connected. 

To change which Deco is Main Deco, follow this document: https://community.tp-link.com/en/home/kb/detail/281

  @Huge85 

You can change the location of the main Deco in the app. That's just a text field and has no influence on the functioning.

Start the app --> Click on "Internet" --> Select your Deco --> Click on the pencil. There you can change the location.