This circuit is a prototype and is larger for ease of building. It will greatly shrink if I decide to move forward. Second, I employ ESD circuit protection. Third, I utilize proper logic voltage level shifting. Fourth, I generate the mixed logic voltages on the board. Fifth, I use a PIC microcontroller but not the one you list. I have spare pins for other features I plan to add. This is a properly engineered board and not a seat of the pants design.
For the record this would require no modifications to the ATARI 2600 or 7800 consoles. It would just plug into the joystick port on the ATARI 2600 or 7800 console.