Okay, now that I'm home, I can reference the points better. First, her statistics are as a Great Gold. Yes.
Breath weapons as Great Brass plus spiral of degen.
Spell Immunity: Hers is weaker than Bahamut's...spells below 5th level (in other words, spells of 4th level and lower) do not affect her. Bahamut gets immunity of spells up to and including 5th level. Of course, they upped Tiamat's in 3E also.
In any case, I don't see Aas as a rank 10 god. Looking at her caster levels in MonMyth and other statistics (breath weapon damage, etc.) compared to Bahamut, I would rank her as a rank 8. (or even 7, but I stuck with 8), and Faluzure as rank 9.
I still have some problem with how you assigned stats, but I have a problem with Tiamat's official stats too (why is she less wise than a Great Red Wyrm?). So, anyways, I re-did all of the dragon gods right now.
Anyone have any ideas about how to handle monstrous deities in general? Dragon gods are obviously not much stronger than their respective races compared to humanoid gods. But then, they have dragon hit dice and not outsider hit dice.
Which gods should have outsider hit dice and which gods should have monster hit dice?