alrighty then. I will have to take some of drowdudes advice on this. hmmm... d10 hp, breath weapon usage should probably go down to twice a day for each form. 5/+1 damage reduction. skills should be those of a warrior, and goes down to 4 per level. no template required. This probably does qualify more as a main class rather than a prestige class. Good saves should be will and fortitude(to reflect a dragons not high dexterity).
However, I still like the idea of the Brood sword. However, the forms that add HD to damage should be changed somehow. I don't like combining multiple types of HD when I roll for damage.
Increased strength as the PC gains levels would be interesting, but how would damage be determined?