Hi Elliott, This is a great breakdown and very generous in sharing your process and insights, you came a long way from the vending machine days!
Are you planning on releasing the UE4 project to the public? Or only builds? I'd love to play around with it in the editor if possible!
Enthelity Studios released a new little tool, which can help you quickly convert maps for game assets.
Enrico Tammekänd shared a link to a simple and free map converter for generating your Metallic/Roughness maps for Unity and Unreal Engine. It’s best to be used with Substance Player to generate needed maps, but you can also do the same thing in Substance Designer.
You can download the tool here, for free.