+1 on using the KADE firmware. (Release date in about ~2-4 weeks.)
It gives you 20 programmable inputs, two dedicated inputs (Reset and "HWB"), +5v, and ground.
If you use a Neutrik USB A-B feedthru, you can have the USB B on the outside of the case and plug the AVR into the USB A on the inside. Since the Minimus AVR doesn't have mounting holes, the feedthru acts as the mount.

With the right current limiting resistor, you can use the 5v for some LED admin buttons. (No fancy RGB/animation, but single-color, constant-on LED buttons would work fine.) You can print custom inserts for the LED buttons on Avery 18665 or 8665 adhesive labels.
Scott