Why do you want to create an emulator. You will have to want to code and love it, you want to need to expand your skills. You need to like a challenge. If you want to do it for some type of fame, or respect forget it, it the wrong type of motivation. I would say you can go for a harder system, something that is still not emulated well yet, for if you were emulating a NES, SNES, N64, you might get good information and a lot easier to code .. but you get no motivation that your breaking new ground, also it is nice when people follow and look forward to information, this gives you more motivation.