Here's my honest take on the characters...
Aragorn: Fighter 8/Ranger 8
Legolas: Fighter 10 (Emphasis on archery feats)
Gimli: Fighter 10 (Emphasis on melee feats)
Gandalf the Grey: Wizard 15 (Half-celestial template)
Gandalf the White: Wizard 17+ (Half-celestial template)
Boromir: Fighter 8
I didn't include the hobbits, since I feel that they would mostly be low-level commoners (Pippen and Sam) and aristocrats (Frodo and Merry both come from wealthy families). Pippen and Merry might have a couple of fighter levels, working for Gondor and Rohan like they did.