The remote control client will just be another Adafruit Feather nRF52840 Express board. The board comes with a built in NeoPixel and a push button switch so no external components will be required. It also has a LiPo battery jack and charging circuit so the remote control can be battery operated.
Adafruit provides free modular case designs on Thingiverse to house the Feather boards. The STL files are easy to modify and 3D print.
Here are the 3D printed parts for the remote control.
The bottom container holds the battery and an on/off switch. The default design has a mini slide switch. I modified the design to a mini rocker because I prefer the more defined throw. When the switch is turned on the battery will power the Feather.
The 2 modular containers snap securely together. I drilled 2 holes in the grey case lid. I inserted a black nylon screw through one hole and secured it with a nylon stand-off. It will actuate the built-in push button switch on the Feather. The other hole holds a segment of 2mm end glow fiber optic filament. This acts as light tube for the built-in NeoPixel on the Feather.