This hack looks really cool.
What you should do to your hack is expand the memory space of the ROM to 64MB. This way you can keep all the original characters, stages and music and you can expand on them by adding the new characters, stages and music that you want to add to the game without replacing anything.
Are you planning to add the three characters that Sakurai wanted to add in the first game but he couldn’t because of time constraints: Bowser, King Dedede and Mewtwo.
Are you also planning to restore the original Japanese sound effects that was taken out of the American version back to it as well?