0x07 is Stage 8, which is the final one. Anything after that is normally inaccessible and just results in an endless arcade run until the "kill screen" is reached at Stage 16777216, but I left it in there in case anybody wants to start a pseudo survival mode.
As for the crash, it seems to be caused by the word at 003A2D38 temporarily being set to FFFFFFFF and then reset to 00000000 after pressing start, but having the cheat enabled prevents the upper three FFs from resetting, resulting in an invalid stage number that crashes. I don't know how to make the cheat affect the entire word instead of just the lowest byte.