There is an existing spell that protects you and your engaged allies from fire, and that seems like a good investment for anyone planning to hurl around Flamestorm recklessly.
Clarification: you're probably thinking of "Aqshy's Aegis".
That spell only grants immunity to "non-magical" fire.
(Against magical fire it just adds two soak.)
Yep, that's the spell I was thinking of, and bonus soak is what I meant by "protects".
That spell's specific provisions for immunity to non-magical fire, but only giving bonus soak against magical fire, strongly suggests that Bright Wizards are NOT automatically immune to their own fire magic, which was what the OP was asking about / asserting.
2.b: I do believe the bonus damage from the aqshy order card would apply every time a recharge token was removed.
But those in the conflagration could move out of it. I know I would not stay and fight within a flamestorm, I'd use a manouvre and get out of there first moment I could. So in most cases the flamestorm would only damage someone once anyways, if they are not stuck for some reason. As soon as you move out of the engagement where the flamestorm is raging you won't be damaged by it.
I agree the official/implied rule is exactly as you state: the bonus damage from additional power applies to every instance of damage. I don't like that (mostly-)official answer because it seems out of line with how much bonus damage a single power provides for just about every other Bright Order Spell in the game, but my plan is definitely to use the rule as written/implied. The Bright Wizard at our table has been feeling overshadowed by the Troll-Slayer and the Pistolier/Knight/Marksman, and a high-damage AoE should help even the score.
It still makes me a little nervous, though. You almost had me convinced that I shouldn't worry about it because only an idiot would stand around in the fire. Then I got the card out and re-read it. The comet lines basically prevent the target(s) from retreating, and since it's a Rank 3 spell, the odds on a comet are around 48%.
On the red side, a comet means you can immediately remove two recharge tokens from the card. So 1 power does 2 bonus damage per person in the area or engagement at the time of casting, before they can do anything about it.
On the green side, a comet means the fire follows the main target around and there's nothing they could do about it, so 1 power could potentially do 6 bonus damage to them over time. Unless the target is a Tzeentch Sorcerer with "Destroy Magic", death is pretty much guaranteed... then again, that's technically true even if they have high soak and only take minimum damage each turn. Wow. Good spell.
I just remembered that PCs can spend a Fortune Point to remove 1 recharge token from any recharging card. So if you have 3 Fortune available, Flamestorm hits every target 3 times before any of them get to move. Really. Good. Spell.
The text implies either a target area or an -engagement- so I'm having trouble thinking it was meant to hurt everyone, especially since Great Fires of U'Zhul's chaos star effect is "you hit each other character in the engagement, friend or foe, for 2+ Int damage"
Great Fires does specify "friend or foe" in the Chaos Star line, but it's also more specific when it talks about beneficial area-effect damage. Great Fires is normally a single-target spell. It only does area-effect damage if you raise the difficulty (above that of Flamestorm, I note) and still scores boons, and even then it's a very small amount of damage and specifically states that affects "each other enemy" in the target's engagement. In my eyes, neither the boon nor chaos star line sets any sort of precedent for Flamestorm, because they both use very different language than Flamestorm.
Even without such a precedent, Flamestorm outperforms Great Fires in nearly every way (higher damage, more targets for lower difficulty, greater range, guaranteed kill on the green side, ability to block a chokepoint, etc) even if it is dangerous to your friends.