Set in between the prequels, explore a bit about how the Obi-Wan / Anakin relationship gradually went sour.
Set before the first movie, explore Qui-Jon Jinn as seen by Obi-Wan - and how that affects Obi-Wan later when he tries to apprentice Anakin despite everybody else's objections.
If you set this movie during Luke Skywalker's childhood, you have to completely obscure the "Jedi stuff" that would draw fans and casual watchers in the first place.