I beat the game with my highest character being a 36. I only fought the bosses and chest monsters. NO RANDOM BATTLES. It wasnt as hard as I thought but some monsters did give me trouble. Theres a nice strategy to use too when only fighting bosses and it has to do with the chest monsters. :)
Now im going through with only Cecil and the only part that gave me trouble were the doors in the underground crystal cave. Ninth Dimension sucks! But I got past it after leveling up alot.