so the game "parts" can't just follow the discs. a full game can't end how disc 1 ends.
I think it should go something like:
Part I:
Midgar (introduction, get's the ball rolling, huge. get Cloud, Barret, Tifa, Aeris, Red)
Kalm (introduction to the world map, backstory)
Junon (a little bit of Shinra story)
Costa Del Sol (bright little place after the first 3 drab cities)
Corel (Barret Backstory)
Gold Saucer (huge sprawling theme park that you can spend hours fucking around in, get Cait Sith)
Gongaga (a random town? nah, some backstory about Zack and some important story-driving Shinra stuff. oh and throw acquring Yuffie somewhere on the path to Gongaga too)
Part II:
Cosmo Canyon (re-establish story; learn about pivotal info like the Lifesteam, etc. perfect place to start pt 2)
Nibelheim (the fuck is happening? this town's burned down. get Vincent)
Rocket Town (Shinra sucks. get Cid.)
Temple of the Ancient (Cloud goes crazy #1)
Forgotten City(some important story stuff. I forget what happens here)
Icicle Inn (some backstory on the Ancients, etc.)
Gaea's Cliff/Crater (Cloud goes crazy #2)
Part III:
Wake up prisoner in Junon (get your party back, get the airship)
Mideel (find Cloud and just put that part where he "find himself" here as well. no reason not to. introduction of Weapon)
Scavenge the world for the Huge Materia (this part could be huge and crazy, or they could just contain it to going back to Corel, Condor, Rocket Town, and hitting up the Underwater Reactor. get Submarine)
Wutai (gotta shoehorn it in somewhere? and now that you've got the Leviathan Scales...)
Gelnika (final battle with the Turks?)
Return to Midgar (kill Hojo and the rest of Shinra)
Crater (kill Sephiroth)