Mixbox from scratch

Just wanted to get ideas from you guys on how to go about this. Wanted to make my own mixbox from scratch. Already done both stick and hitboxes but really got curious about having keyboard keys on my directional buttons. My main problem is that i dont have a clue on where to start with the buttons as i have not tinkered with a keyboard before (although have removed and swapped keys as a prank).

If someone has already made one before can i ask for some help. Thanksimages%20(1)

you can try this out.