Thanks very much! I have some keyboard pcbs available here: https://www.tindie.com/products/15575/
The case has some extra room inside, I'm sure you could stuff more components in there. Besides the space available you could modify the back lid to allow for more space. See here for fusion360 models: https://github.com/AnthonyDiGirolamo/teensy-thumb-keyboard#cases
One thing to note is that the display I chose, the https://shop.pimoroni.com/products/hyperpixel-4 uses almost all the GPIOs available on the raspberry pi. Only one i2c connection is left available.