So I'm starting a character based on this blurb written by my DM:

Astaroth. Carver of the World. Messenger of Death. Self proclaimed King of Creation. 50 years ago, a cataclysm swept the planet and its name was Astaroth. The peoples of the world attempted to stop him, but they were not prepared. All but a few of the humans and elves were wiped out. Half-Breeds began to overtake and rework all major cities and locations. The Demon Spire was built. The dwarves retreated underground and have not been seen in 20 years abandoning their allies at a crucial point to protect their own. Any not of the half breed are hunted down and either put to work or used as playthings of the Hierarchy. This is the world you live in. This is home.

I'm supposed to come up with a character (class, background, and general personality and appearance). I am set on playing a dragonborn. I haven't played 5e except for a short stint through the Starter Edition, though I've played 3.5 a fair amount. So far, I want her to be from an isolated citadel on the side of a mountain, just under the snowy cap. Its a self-sufficient temple to Bahamut, and the residents are true metallic dragons (Copper, Gold and Silver) and their kin (Dragonborn, half-dragons, pseudodragons, etc.). The dragonborn (in my head) are made from shed scales of the ancient wyrms that are planted like seeds and grow a plant, similar to melons and pumpkins that grow eggs. Once the egg is 'ripe', its harvested and set into an alter fire before a statue of Bahamut, where he protects the eggs until the hatchlings emerge. My character in particular, Daremisha, was planted as three scales, one from each of the ancient wyrms of the citadel, so her coloration is coppery, silvery and golden, and her features are mixed (horns, whiskers, etc.).

This is what I have of my response backstory so far, having decided the origin of these particular dragonborn:

"When Astaroth plagued the world, picking apart the fabric of life, they were blissfully unaware of the horror culling the humanoid life below the clouds…until one day, a poor soul came up the mountain to the elusive ‘gods’ who lived there and spoke of the calamity that had befallen their land, their home and their family.

The good ‘gods’ of the mountain, the true dragons, were outraged. They summoned the Dragon King at his alter, and his platinum form in all his scaly glory manifested before them. Bahamut had heard of this Astaroth’s wrath across the land, but thought it better handled by the higher powers; his were much more limited in their potency and variety. But, he offered, if there was one among their ranks who would step forward and be his sword against this dark scourge, he would grant a measure of his powers and a blessing.

One small female dragonborn approached him, her head bowed, hands folded before her as she bowed deeply. “I would like to be your sword.” She was coppery, silvery and golden, showing the mixed heritage of the sacred citadel. “My name is Daremisha, daughter of Cidden, Nferiti, and Falilah. I wish to wield your sword and cleave the enemies from such kindhearted people.”

The Dragon King nodded, reached an ancient claw forward, slowly morphing into an elderly human man, clad in dirt-stained farmer’s clothes. He continued moving toward her until his hand rested upon her forehead. “My daughter. The daughter of three. I will grant you my strength and my wisdom. You are my sword, my Talon of Justice, and I will aid you in your times of need, while you aid the poor souls of this world in their time of need.”"

I want them to be religious, especially in following Bahamut to wipe the demon scourge from the land. My problem is whether they should be monks, paladins or clerics in this setting.
P.S.: It should also be noted that I noticed a similarity between Asgorath (or Io) and Astaroth.