How do I created custom Shavian keycaps for onboard?

I am learning to use the Shavian phonemic alphabet for English. It is easy to handwrite but I want to create an onboard layout that shows:

• both unshifted and shifted characters on each keycap without having to click the shift key to see the shifted characters
• the names of each Shavian letter next to the character on the keycap
• based on the standard US layout excluding the top row of function keys (e.g. F6, etc) and the numeric keypad
• including the Insert, Delete, Backspace, Home, End, PgUp, and PgDwn, and the arrow keys Up, Dwn, Left, and Right

Finally, is there a tutorial book or article that relates the XML layout file to the visual appearance of a keybaord?