I am a balance wizard and a mom, so you will not get a really technical explantion from me. Equipped the tower shield all through Celestia. It is very powerful and I loved it. As you get to Wintertusk and Zafaria you may want to upgrade it. I always had as many green sprites for healing as I could. Healing Hands for helping yourself and others. Your single and double blades, at least three of each type. Blast & Hydra when fighting a balance enemy or boss, Judgement & Ra. Power Nova is good. Weakness. And definately at least 3 minions ( not the mander). Some cards from your secondary school. Mine was death so I put on hexes and feint to upgrade my judgement. Absorbs and shields help too. Your clothes should always be upgraded - look for things with pips and damage. The real gamers will be of some help now. Hope I could help you.
If you're level 55 you're allmost high enough level to get Carax Strongthread's gear recipies in Sudrilund (Wintertusk). That gear is some of the best gear in the game (better than waterworks imho). Why am I talking about gear? Because with his gear you get a blade and trap in your school. Those blade/traps are a "different" spell from your learned version, and will thus go off at the same time. I got thru Celestia and most of Zafaria just by casting my blade, my blade from the gear, and then attacking on the next turn. More often than not, everything was defeated by turn 3 or 4 (depending on when I got the pips to attack).
But you only get one copy from the gear, so to insure you see that blade in turns 1 and 2 (3 max) you need to run a small deck -- very small. My "General Purposes" deck has only 9 cards in it -- that's it.
Two copies of my best attack all spell Two copies of the best sun spell I have for damage Two copies of my blade Two copies of my trap One reshuffle
Now I'm ice and not balance, so the numbers are a little different, but if you got the balance gear (50% bonus to damage), used monstrous (+175 damage) and cast your balance blade (+25% damage) and the balance blade from the gear (+30% damage) you should be doing around 1550 damage to all with nova on Turn 3 (assuming you get the pips to cast). Wait another turn and cast bladestorm (+20 damage) and you'll be doing around 1875 in damage to all with nova.
I'm using a starter deck, so 13 cards and 5 treasures. It contains 3 sandstorms, 3 colossal, 3 availing hands, 1 elemental blast, 1 balance blades, one judgement and a reshuffle. Last spot can change according to needs for special fights. Treasure are either other blades, or vengeance, amplify, infallible cards (for the piercing). Sometimes i fancy putting a trap or two there and swap my blast for a hydra (against shielding enemies).
In your case, i would just swap the star treasures with sun school ones, since you trained schools the other way round than I did, and put star spells in main side of the deck.
As you can see, shields are not really there, as i don't use them anymore - I have a quite high power pip chance, and healing boosts from both the knife and the ring. I would suggest if you don't, to use the empty spot for a power play spell, and to keep that healing aura handy as well.
With this setup i fought most areas in celestia (except a few bosses and last dungeon), wintertusk (including last bosses, excluding the previous ones), waterworks (except the bosses) and zafaria (except last dungeon).