I think I am done with the layout.
To make this board more versatile, port P1 is connected to the header, so instead of USB->MIDI, this board could also be used as logic analyzer or USB->Power Board/Relays, etc.
There is a programming header, BSL header, 3 LEDs (one USB power and two general use,) opto isolator and buffer for MIDI In and Out.
The two drill holes on the left can be used for wire tie, in case wires are soldered directly to the board.