i'd level up more to around 55-65 but make sure you have curaga. i was struggling with necron too but as soon as i went to the black mage village and taught garnet curaga, i won.

amarant is a very useful character because of his aura ability. i would have found the game harder without the aura ability. if you use all of amarants tursn casting aura and possibly give him haste, all of your characters will have auto-life so if neutron ring kills them or grand cross dooms them, they'll be brought back. if all four of your characters have aura, use amarant to throw powerful items. you wont need them when the game is over after all.

what characters do you tend to use?