Try lovemyswitches dot com. The "switches" mentioned are not keyboard switches but guitar ones. However, the knobs make for fun window shopping and are usually under $5.

Love the case. I'm not an expert in color theory by any means, but given the deep rich crimson color, you might want to consider a keycap set with modifiers that are lighter than the letter and numbers. That way you have a contrast of dark/light/dark.

Also, you can play around with swapping out the encoder knob. Take a look at guitar knobs - there are a number of cool options under $10. You'll want to check the encoder shaft size, but 6mm inner diameter knobs are usually a safe choice. Make sure you check the outer diameter - I'm eyeballing it, but 12-15mm would be the max you could get into the recessed area.

Cassette storage for the win! I remember loading C64 games that way. Start it up, go eat lunch, then come back and play!