Hello @DMarkwick, welcome to the community!
You’re totally on the right path but I noticed you’re missing some Layer Info Objects there.
A layer info object is an asset that contains information about a particular Landscape layer. Every Landscape layer must have a layer info object assigned to it, or else it cannot be painted. You can create layer info objects from the Landscape panel.
Please, check this documentation page to find all the informations you need: Paint Mode | Unreal Engine 4.27 Documentation (just search for “Layer Info Objects”).
Let me know if you have any further question!