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.