Replacing Gogo with Daryl

I'm preparing to start my first real hack, and just want to make sure I'm going about things the right way. If I wanted to replace Gogo with Daryl (as in: change sprite entirely, add small dialogue beforehand, and make her special ability JUMP), what steps would I take?

As I understand it, I'd need to:
   replace Gogo with Daryl in a Sprite Editor,
   rewrite the dialogue with Gogo into a longer script,
   and make Jump a permanent skill rather than a replacement for attack.

If possible, I'd love to make Jump her only way to attack as well as giving her a secondary skill, but that seems like extra complication for something while I'm already on shaky ground.