> I thought it would be simpler to start with a Game Boy Advance or an 8-bit processor like the 6502
The 8-bit processor will be much more approachable. I have worked on my GBA emulator for around one year now. Before that I tried the classic GB and its 8-bit CPU was so much easier to implement. The GBA's ARM7TDMI alone took me 3 months to complete, even with extensive testing [1].