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!
Take a look at the complete set of the Caps and Tubes pack by Mark Tomlinson that contains a collection of 75 Sub-D kitbash parts for use in the Polystein Kit for Modo.
All mesh are quads and contain color separated regions for easy selection.
You can also buy each part separately:
Again, the Polystein Kit is a toolkit consisting of an array of all-quad SubD mesh presets that can be seamlessly added to a model making mesh detailing incredibly easy. This powerful toolset positions, scales, orients and auto-stitches these mesh presets to your active mesh relieving you of the tedious process of doing it manually.
You can find more details on the pack here.