Thanks! Plate is aluminum. I brushed it with sandpaper and applied some metal polish for a shiny brushed look.
I got the case from JLCPCB with their cheapest resin (8111X). Got it for only one dollar including shipping lol thanks to the $7 coupon you can get from sharing 3D models. Out of the box, fairly sturdy. It was semi-translucent white but a bit yellowish and ugly, so I spray painted it.
Also, there's a commercially available CH552T dev board for about a dollar. I actually use this for development: https://www.aliexpress.com/item/1005004141926425.html
Even cheaper if you buy just the chip. Just add a USB connector and two capacitors then that's it. No crystal, flash, etc. needed. A CH552G goes for about 30 cents: https://www.aliexpress.com/item/1005003402478164.html