Here's the rundown of the Crew Episodes and how to unlock (most) them, there's 57 total:
Straw HatsLuffy: Beat the main storyline
Zoro: Clear Chapter 3-6
Nami: Clear Prologue-2
Usopp: Clear Chapter 3-4
Sanji: Clear Chapter 3-6
Chopper: Clear Chapter 1-3
Robin: Clear Chapter 3-4
Franky: Clear Chapter 1-1
Brook: Clear Chapter 1-3
PlayableSmoker: Clear Prologue-2
Jimbei: Clear Chapter 1-2
Marco: Clear Chapter 1-4
Kuzan: Clear Chapter 2-1
Perona: Clear Chapter 2-2
Hancock: Clear Chapter 2-3
Ace: Clear Chapter 2-4
Kuma: Clear Chapter 3-1
Mihawk: Clear Chapter 3-2
Crocodile: Clear Chapter 3-6
Buggy: Clear Chapter 3-5
Garp: Clear Chapter 4-1
Whitebeard: Clear Chapter 4-2*
Law: Clear Chapter 4-2*
Eneru: Clear Chapter 5-1
Kizaru: Clear Chapter 5-1
Akainu: Clear Chapter 5-2
Teach: Clear Chapter 5-2
*Only if you beat the stage without killing Whitebeard. see my guide for the following Trophy:
Alternate CharactersLuffy - 2 Years Ago: Clear Chapter 5-2
Zoro - 2 Years Ago: Clear Chapter 5-2
Nami - 2 Years Ago: Clear Chapter 5-2
Usopp - 2 Years Ago: Clear Chapter 5-2
Sanji - 2 Years Ago: Clear Chapter 5-2
Chopper - 2 Years Ago: Clear Chapter 5-2
Robin - 2 Years Ago: Clear Chapter 5-2
Franky - 2 Years Ago: Clear Chapter 5-2
Brook - 2 Years Ago: Clear Chapter 5-2
Teach (Double Ability): Clear Teach's Crew Episode and all the Straw Hats Crew Episodes.
Support OnlyJozu
Vista
Ivankoff
Mr. 2 Bon Kurei/Clay
Mr. 3
Arlong
Hatchan
Kaku
Jabra
Lucci
Blueno
Don Krieg
Lapin
Wapol
Sentoumaru
Pacifista
Magellan
Hannyabal
Minotaurus
Gecko Moriah
I deeply apologize, I can't remember when you unlock the Crew Episodes for the support-only characters. If anyone can help me, please send me a message other than a comment.