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!
The Wolf team (a project dedicated to Blender) has a nice pack of free PBR materials for you to check out. The materials here would work great for all kinds of scenes, so don’t miss this chance.
Here are some preview images to get you excited:
Make sure to read this guide to get started.
The pack is updated gradually, so bookmark this page to get more materials.