The big battle during White Night:

Fuego
Force Shield, extended and made reflective (it's notably more expensive than earlier versions)
Forzare as a area attack
another Force Shield which lasts for multiple exchanges
a rift to the Nevernever (which is elsewhere said to be very magic-intensive)
brings up the shield again
another Forzare blast, with Hellfire, multiple targets
a massive fire spell that turns an entire area to molten stone
another shield activation
and one final shield powered by Lara's kiss, which might involve a consequence - although there is no textual evidence of any lasting effects

Even assuming Sponsored Spellcasting handled the fire, and one of the force blasts, that's an absolute minimum of six castings.  Assuming that Harry accepted mild consequences (which there is absolutely nothing in the text to suggest) he'd still have made four normal castings, which would fill his mental stress track completely.  Assuming he didn't additionally extend any of the durational spells - that would put him way over the limit.

(I'll point out that Ramirez casts many potent spells with multiple targets that are nevertheless lethal despite having some serious injuries which would preclude his accepting consequences to cast, too.  He does not seem to possess any kind of Sponsored Spellcasting.)

And, of course, he was subject to a massive psychic attack which would also produce stress and temporarily incapacitated him.  Which by the rules he would be far more vulnerable to than most of the people in the battle, because he'd been casting spells, and in the RPG rules that produces stress on the mental track.

Have you actually ever sat down with the novels and worked out how many spells Harry throws around in the equivalent of a 'scene'?  Particularly in the later novels, in which it implied that either his capacity for magic has increased or he's become much more efficient (or both, of course).

Four or five spells doesn't cut it.  And we're ignoring the point that some spells are inherently more magic-intensive than others, regardless of how they're customized.

If I might switch continuities for a moment:  in Doctor Who, there is a villainous military space station that is named Demons Run - which, when it's pronounced, would likely be interpreted as Demons' Run - the place where demons have free reign.

In actuality, it's a shortening of an old saying:  "Demons run when a good man goes to war."  The meaning of the name is in reality entirely different from what we would first assume.

No supernatural entities are going to name urban regions after themselves.  It's far too obvious.  The names are clearly worn-down remnants of mostly-forgotten meanings.  Find what those original ideas were and you'll know what's there now.

I don't think we know about them for anyone to attempt a write-up.  Seriously:  a sentient, mortal race capable of casually moving cars and with immense supernatural abilities that don't work in the same way as (or aren't starting off from the same perspective as) human magic?

We'd probably need new mechanics.

I just figured that each 'school' of thaumaturgy is its own theme.  It confuses me.  Couldn't a 'summoner' also do wards but his wards would involve patrolling sentinels that he'd summoned?

  I wouldn't interpret it that way.  A summoner wouldn't be able to manage anything more complex than the basic charged circle - the sort of thing that anyone with even a little power can manage.  He would be able to touch the other aspects of thaumaturgy only to the degree that they're part of summoning.

Now, what he could talk or bind the summoned creatures into doing for him is another matter...

Harry's made Ghost Dust before, which mechanically is a potion.  Don't be too limiting - but consider that Harry needs some strange and exotic ingredients to make potions, and sometimes those requirements are a problem.  (He hasn't been able to store sunlight for years, now.)

If the player can't find the right recipe to make the potion that is desired, or can't tell an interesting story about how they managed to create it, I'd say they don't get the potion.

A lore declaration doesn't cost a FP.

  I looked it up:  either a FP or a successful Lore roll.  That's still somewhat iffy.

Primarily, that you can't do things on the spur of the moment, unless perhaps your group permits the optional rule that you can define what potions you have on hand.  Even then, I think it costs both a successful Lore roll and a fate point.

Consider also that potions (in whatever form) are physical objects which can be taken away from you.  Also, many thaumaturgic effects don't actually translate well into potions.