Your Crypto Countdown circuit deserves to live in a rugged-yet-age-worn case to give it that action thriller feel. You can find a vintage case that's ready to go, or start with a brand new case and distress it with watered-down paint.
With the case closed, apply a heavily watered down black acrylic craft paint wash with a brush and let it dry overnight.
You can wipe off paint in some areas, and leave it nice and dark in the recesses and crevices.
To go with the Soviet KGB theme, you can spray paint a red star onto the case using a stencil. I've included a star template in the files linked to here, which you can print and cut out to trace onto mylar or cardboard stencil material.
Start off with some gray primer, then once that has dried, spray on your logo.
If your case came with pick-and-place foam, you can remove it entirely, or cut it out to fit the parts.
The switches, display, buzzer, indicator LED, USB port, and power button all need to be mounted to a panel. You can do this in a variety of ways -- I started out with hand cut cardboard for prototyping, then laser cut cardboard, baltic birch plywood and finally acrylic for the final prop.
There are a variety of ways to cut the panel, from hobby knives, to hand-held coping saws and drills, to bandsaw, CNC machines, and laser cutters. For highly professional pieces, you can have custom panels made by a service bureau or online panel maker.
Download the files linked here and print them out as a template for cutting, or to drive a laser cutter or CNC. Or, use it as a guide to model a file for 3D printing.
In order to add the graphics I ran a second etching pass on the laser cutter to lightly score the acrylic, then painted them with white acrylic craft paint and immediately wiped it off. The paint comes off of the smooth surface easily but stays in the rough etched portion of the graphics.
I also ran a third, low speed and high power etching pass on the section that holds the missile switch safety covers in place. This prevents them from twisting around at all. Alternately you can add a bit of glue to hold them in place, or turn the nut hard enough to bite into a softer material such as wood or cardboard.
For added support to keep the panel from flexing I added a second, inner panel with cutouts to clear all parts and screwed it to the top panel using the 2.5mm nylon screws and nuts.
Now you can mount the parts in your panel. Remove the top nut and safety cover from each switch, turn the lower nut up to the midway point of the shaft and then push the each toggle switch through its respective panel hole, lining up the thread groove with the panel hole tab.
Then, place the safety cover over each switch shaft, and tighten the top nut into place.
You'll mount the FeatherWing-Feather-FeatherWing sandwich to the panel using nylon standoffs. Make an appropriately sized standoff by screwing together as many as needed to mount the display flush with the panel.
Then, fasten them to the panel with screws from the top, leaving the threaded standoff ends to affix the FeatherWing.
Test the FeatherWing mounting position but don't screw the nuts into place yet, you'll still need it free to connect the power button wiring.
Unthread the the illuminated on/off power button's locking collar and then feed the wires and JST cable through its hole on the top-side of the panel.
Then, screw the collar back on, securing it in place.
Re-attach the power button's wires to the screw terminals (this is easier to do before the FeatherWing is mounted) and re-connect the JST connectors.
Place the NeoPixel LED into its holder, then push the holder into the panel from the top side. Then connect the 3-pin connector to the LED's legs, being sure to mind the color order. Remember, the long leg is the GND terminal.
You can gently bend the legs to a 90 degree angle if you like for better clearance with the case foam.
For re-programming and battery charging (the Feather has built-in charging circuitry), you'll want to be able to still plug the Feather into USB after the case is assembled. The panel mount USB connector allows us to do just that!
Fasten the USB panel mount using two 2.5mm nylon screws and nuts, then plug the male end into the Feather M0.
Screw the FeatherWing sandwich onto the standoffs with the four nylon nuts. Then, connect the battery, and place the panel into the case. This will be secured by a nice, tight friction-fit -- just be sure escape room players know they aren't meant to disassemble props to solve them! You can also choose to more permanently seal the panel with glue or fasteners.