How about looking at it this way: "hacking" is not some thing where you randomly change numbers in a hex editor and make magic in video games. "Hacking" is reprogramming the game. Pursuant to this, you need to have the skill to write your own computer programs before taking on hacking.
But just so you know, you've no idea what you're getting yourself into. A major time sink of mind-bending frustration... there is a reason there are like 20-30 games with full translations sitting around and no one has yet completed their implementation. Each game is a labyrinth unto itself. But if you insist, there are gobs of resources on this site for the task. One tutorial teaches you how to create sprites on the NES. Elsewhere, you'll find complete ASM dumps for entire games. You'll find things go much, much deeper than the "accumulator".
Oh and one more thing: the locations of the experience yields has already been discovered. It should be on Datacrystal or if not there, in the Dragon Warrior shrine at RPG Classics. And if not there, check the Game Genie sites to find the exp tables themselves.