Forget the profit/patent thing for now, as it's really not important. You're probably doing this for fun, not for money.
A few things to consider:
-What hardware are you going to use and why?
-How "deep" into the hardware are you going to go? (Are you going to look at it at a module level, chip level, or even transistor level?)
-What operating system are you going to use? Will it be your own? If you're using a micro controller, you may not need to consider this point.
-How are you going to handle the screen output?
-How are you going to handle controller input (or any other input)?
-Are you capable of programming a rendering engine?
-Are you capable of programming a game?
-Do you know enough about chip instruction sets, and how they cooperate with each other?
Just some basic questions... It really depends what you want to do...
Maybe my project could help you a bit : I am making a "game console" right now actually, it's a simple C8051F320 micro controller connected to a custom made 8x8 RGY LED matrix. The matrix is made up of a bunch of shift registers, so I have a serial display data input, and 4 control bits (in total 5 bits control the screen). There are a total of 128 LEDs (64 2-colored LEDs), and I want to update the screen 15x a second, plus have a brightness control of 8 stages (controlled by a PWM signal), so the output frequency must be 128x2x15x8=30.72 kHz. The micro controller I chose has a clock speed of 5 MHz, each instruction taking 12 clock cycles. So 5000000/12=41.6 kHz, which is more than enough to control my screen and many other things. I also plan to make 4 game controllers for input, each having 8 buttons. Because the micro controller is limited to an 8-bit input, the controllers will be multiplexed.
And that's about it

I could provide more technical data, but that would just be spoon-feeding you, and I'm sure (from what I've heard of you for now) that you're capable of coming up with your own circuit or layout. You should make this a thread where you update what you're doing, and post diagrams and things
TheComet