You don't consider "the circumstances of his death" to be declarations?  Blood seems to allow for lots of useful 'circumstances' by itself.

Which could be counted as "double-dipping", since you're already getting completely free tags on every drop of blood you've shed (ie, consequences).  But I'm just suggesting that interpretation for the consideration of the readers; it's not necessarily clear to me that my interpretation is absolute RAW.

But perhaps you're correct...in that case Death Curses aren't going to be very effective unless the wizard chooses to concede (and die) unreasonably (IMO) early.

Maybe ... maybe not.  It could be argued that Maggie's death curse was nothing more than a long-duration aspect (maneuver) placed on Lord Raith, and endlessly compelled by the GM.  Or perhaps a couple of stacking aspects.  In either case, such a spell wouldn't take all that many shifts to create.  What it would mean (if the interpretation is correct) is that you can't simply vaporize your killer with your death curse -- you have to be more subtle to make it really hurt.

The DC sidebar could also be read as not allowing declarations, by the way.  It seems to me to indicate that while thaumaturgy normally allows four components of preparation (invoke aspects, make declarations, accept or inflict consequences, and skip scenes), for the death curse "the components of preparation are the circumstances of the wizard’s death—all of the consequences he has can be tagged, and he can inflict more upon himself if he’s got the space".  It makes sense that skipping scenes is right out, but it also leaves out declarations -- possibly deliberately, on the basis that preparation declarations represent mini-scenes, which there is no time for.

Where else in the game does it allow you to double dip on a consequence or other aspect on a single effect?

How is it double dipping?  There are two mechanics applying here.  First, you may inflict consequences to contribute their shift value to a spell.  Second, you may invoke aspects (if justifyable) to contribute +2 shifts to the spell.  Under the standard thaumaturgy rules, I read it as legitimate to inflict, say, a serious consequence on yourself for +6 shifts, then spend a Fate to invoke the resulting aspect for another +2.  This assumes that you can justify drawing on the aspect to benefit the spell, and that you have too much available Fate and too few available/appropriate aspects.

I can see the argument about timing, and agree that it's not entirely clearly defined.  However, it does state in the Death Curse sidebar that Death Curses count as rituals but with the normal preparation replaced by the circumstances of death (can only tag and inflict consequences, so no sitting out scenes!).  But the general thaumaturgy rules allow the various methods of preparation to be "combined in any way you choose" (YS268), which does not appear to be over-ruled in the sidebar.

That said, even though I think the rules allow for you to inflict a consequence then tag it, I think that balance would be better served by allowing the character to do only one or the other.  Meh, tables can work this out as they want.  However, the two likely resolutions work out to:
1) the shift value of all unused consequences, plus two shifts for each used consequence (assuming the order matters) OR
2) the shift value of all unused consequences, plus two shifts for every consequence slot on the sheet (assuming you can use either/both options in the order you see fit)
Take your pick.

As an interesting aside, either option results in stronger death curses from wizards who happen to have extra consequences (from high ratings in the stress-track skills or certain stunts).  Just having the Resilient Self-Image stunt, for example, adds at least +4 (and possibly up to +8, with option 2 above) to the potential strength of a death curse.

I don't have any problem with the basic concept of multi-refresh stunts, assuming that the guidelines for stunts are maintained (ie, stunts are strictly mundane abilities, and marginally less effective point-for-point than "equivalent" powers).

I do agree, however, that building them as trees of one-refresh stunts that build on each other has advantages.

For example, take Hammer Blows.  Instead of having the single stunt for three refresh, why not do something like this:

Hammer Blows I (Weapons) - Choose a type of muscle-powered weaponry (swords or thrown daggers, etc) and gain +2 stress when attacking with that weapon.
Hammer Blows II (Weapons) - Choose a class of muscle-powered weaponry (melee or ranged) and gain +2 stress when attacking with that class of weapon.  Must be purchased as an upgrade replacing Hammer Blows I and for the class that includes the type chosen for that stunt.
Hammer Blows III (Weapons) - Gain +2 stress when attacking with any muscle-powered weaponry.  Must be purchased as an upgrade replacing Hammer Blows II.

Note that I'm not commenting above on your pricing, just splitting the stunt into components building up to the same pricing you used.  By doing it this way, you let people decide the level of commitment they want, and allow them to smoothly upgrade as desired.  It also has the side benefit of making it a bit easier to see how the costs are laid out.

Yup, I was wrong.  So I guess that would actually make the potential range from 8-28 (more if the character had extra consequences).

The book's version only affects stress and consequences.  I guess Sanctaphrax's version might include maneuvers, if the GM chooses to, so the new version of immunity makes immunity even more powerful, since you can't even perform maneuvers against the target (in order to escape, for example).

How many demons (as opposed to Fallen) do or do not have Hellfire is speculation.  Even if none of them do, however, RAW claims that all Fallen do, and WoJ supports that.  So if you go with the Pope's assessment on the Fallen population (and I'd argue he is more an expert than any of us on this forum), then that's more than 133 million sources of Hellfire.  That's a lot of Hellfire -- and also a lot of speculation, though based on studies made by the best experts in the field I could find.

Of those Fallen, we know that in DF 30 of them closed escrow on coinfront real estate, and RAW/WoJ indicates that all of them have access to Hellfire.  Of those 30, only several are known to have granted Hellfire to their human counterparts, as recorded in the novels and DFRPG.  That list includes Thorned Namshiel, Saluriel/Quintus, and Lash/Harry.  One third of those (Lash/Harry) are not considered affiliated with the Order of the Blackened Denarius.  It might also be worth noting that in the case of Lash/Harry, Hellfire was being granted not by a Fallen, but by the mental shadow of a Fallen.

Bottom line, I still disagree with your sweeping statistics, based on a sampling of about 0.00000225% of the Fallen with only 67% success rate.

However, if you accept my propositions, that the Order represents the greater part of conduit entities for the granting of Hellfire to mortal would-be-practitioners, and if mortals having entered into a pact by way of members of the Order would be viewed as associates of the Order (and thus granted some protection as members under the Accords), then, while not all users of Hellfire would be explicitly protected by the Accords by way of the Order, the mere plurality of mortals so protected would give implicit protection to the rest by way of the fear that pursuing them would be pursuing a protected individual regardless of the fact that that protection is only perceived and not real.

I can't really agree with this, either.  First, I suspect that the total number of demons in existence is many times more than the 30 Denarian coins.  Apparently one estimate by Pope John XXI (before he became Pope) was that 133,306,668 angels fell with Satan.  I have no idea how he came up with that estimate.  But since 133,306,668>>>30, there's a lot of room for noise in that estimate and still result in an overwhelming majority of demons who do not reside in coins.  Of course, since this is DF that we're talking about, we'll have to ask Jim Butcher how many there are (we have seen at least a handful of non-Denarian demons in the novels).

As to the Lawbreakers, as UmbraLux mentioned there's no absolute answer.  I seem to recall Fred suggesting that characters with sponsored magic might be protected from Lawbreakers by their sponsor (the sponsor "takes the hit", possibly at the cost of debt).  Note that that implies that the Law is being broken, but that the caster is being shielded from the effects.  I think some have conjectured that the Blackstaff might work along these lines.