REGISTER TO REMOVE ADS
I've gone through KH1 with just the Kingdom Key and scarce abilities before, so I think I can do this.
Even paying through the game with only the Kingdom Key and NO abilities at all is nothing like playing through at lv1. If you want a real challenge, try going through by killing absolutely no heartless at all (except the ones you are forced to kill, and bosses of course). Doing so will probably only get you to lv 20 or so by the time you get to the final fights with Ansem. This is the closest you can get in the PS2 versions to a lv1 playthrough.
When 1.5 comes out, I think you'll be surprised by just how insanely hard its gonna be to finish this at lv1.
Just out of curiosity, does anyone know what difficulty mode Zero EXP is available in? I'm guessing its only available in Final Mix: Proud mode, but I'm not sure.
On a similar note, does anyone know how and when Sora gets the Combo Master ability? After all, it's not in the original Final Mix.