Design my own arduino PCB

I've been trying to build my own arduino game/teensy full color high res hand held gaming console with an easy to use library so any one can play or build.

I've been working on the hardware but I've since realized wiring takes up a lot of space. So I thought why not make my own PCB with where you just have to solder the buttons and screen and then all the arduino bits and a charger/step up included in the board.

I'm looking at eagle cad but I don't know what all or what kind of parts I need to make it arduino/teensy powered. Like processors and what chips can be used to create Progmem or flash. How hard would it be to make two cores? One to handle program stuff and the other just to process graphics? What do I use for compatible ram?

Questions like the above. Any support would be appreciated.

PROGMEM is what we use to put data into the flash on our Arduino chips. You can use PROGMEM on an Uno.

You want to make a gaming system with high def screen? I would use at least an ARM chip duino at minimum, the latest Teensy might do but an RPi would be better.