Tales of the Green Lanterns in the vein of Thirty Two Short Films About Glenn Gould (or 22 Short Films about Springfield).
Bookended by Hal's origin and his becoming Parallax.
Introduce John Stewart, Guy Gardner, and Charlie Vickers. Save later Earth lanterns for the sequels.
Include actual Tales such as Rot Lop Fan, Mogo, etc. Maybe try to lure Alan Moore to write some new ones... he probably won't take money so offer him, I dunno, something with magical importance. A really, really good snake puppet. Get him to write a Tale about the snake puppet.
Include the Starheart's origin, show Yalan Gur, show the merging of the twos' legacies. Show the lantern made from his ring giving first, death, second, life, third, Alan Scott's power. Give only hints as to why Scott is not remembered by Hal Jordan et al.
Include very brief cameos establishing personalities and gimmicks of some other DC space types. The Omega Men. Doiby Dickles. Despero. Evil Star. Embrace the names or show them as a mix of literal translations and transliterations. Get Alan Moore to help you if you need it.
Get the same actors you used in the Ryan Reynolds movie, but completely ignore the actual events of the movie.
Later sequels will all be anthologies as well, generally introducing a new Earth-based Lantern, showing why they were needed, following up on past favorites (I want a Rot Lop Fan segment in every movie, even if it's a wordless over-the-ending-credits animation). Metaplot moves forward as movies go on.