Looks cool man. The only suggestions I have are that you better triple check your sprites don't get blurred when you blow this thing up to 300dpi, blurred sprites that are the focal point of a piece can make the whole thing look trashy unfortunately. Just a suggestion on your background, you thought about maybe some character art back there, I personally think the 3rd strike Akuma pose would be perfect for the akuma one, the ryu one I'm not entirely sure of.
btw, out of curiosity what gamecube games are you planning to play on this thing anyways? I don't know of a whole ot of games I"d want on my cabinet from my gamecube right now, although I'm sure there are going ot be some really good releases out in the future.