First of all, forget about spellcaster classes. With racial HDs of 8 and LA of +4, he can never, ever, be a descent spellcaster PC (Remember a wyrmling does not have spellcasting ability yet).
He will work best as a melee character. His BAB is -4 lower than usual melee characters of equal ECL and his strength is not so spectacularly high comparing to the warriors of the same ECL. His racial strength modifier is +6. But LA +0 characters, at 12th-level, is raising his ability score 3 times already. A 12th-level Half-Orc has only 1 lower strength compared to him.
But at least he can be a more than descent melee attacker with his 5 natural attacks per turn (bite, claw, claw, wing, wing). Take Multiattack feat in MM and possibly Improved Multiattack in Draconomicon.
As for class, he can either take classes with full-BAB (Paladin?) or maybe Rogue. Yes, sneak attacking with 5 natural attacks will be good.
If I were the player, I will take 1-2 Rogue levels, then take 1-3 Paladin levels. And when hitting ECL 16 (a 12th-level character), take Devoted Performer feat to continue multiclassing between those two classes. And/or proceed to Shadowbane Inquisitor prestige class.
I will not take Vow of Poverty. Actually, a Dragon CAN USE MAGIC ITEMS.
Read Draconomicon and other books (say, Magic Item Compendium). He can even wear tailored armor as per PHB rule. He has natural armor bonus of +7. With a tailor-made magic full-plate, his AC could be really high. Even if he is not proficient in any armor, he can wear tailored mithral chain shirt (no armor check penalty).