I do like your approach. Its very clean and simple. My only niggle is that in the books, evocation does tend to wear out spellcasters. Having Harry continuously blast opponents without signs of fatigue doesn't seem quite right to be, although I agree about fallout and backlash. Much easier solution.

A reasonable niggle... but consider: Sprinting everywhere would tend to wear out a runner - but there's nothing in the fate core rules to enforce that.  If you wanted to make it very clear, though, you could add in a sentence like "Extended or continuous use of evocation tends to be exceptionally tiring compared to even strenuous physical activity; if this comes up in play, treat your effective endurance for spellcasting as your Will skill minus two."

Hm.  For contrast & reference, here's my fate-core-ized version of evocation.

Evocation:
Requirement: A high concept (or, with GM permission, other relevant aspect) indicating that you can work magic.
Cost: One refresh.
Limitations: Evocation should have some appropriate thematic limitations - perhaps you work with, say, just fire, force, and wind.  Work this out individually; a spellcaster whose paradigm is the eastern elements of Wood and Metal would be very different from a hippy wannabe-druid or a retired ectomancer, even if the power is mechanically the same.

Effects:
1: You may defend yourself from attacks using your Will skill - if and only if you have an appropriate aspect placed on the scene, such as "wall of fire", "dome of force", "entropic shield", or the like.  (Note that this will usually apply only to physical combat... but only usually; for example, one could easily imagine a wall of fire justifying using Will to defend against an opponent's attempts to intimidate you.)
2: You may attack with magic using either Fight or Shoot skills, as appropriate.  Working magic at range is difficult, though; you're at -1 for each zone your target is away from you - though this can be offset with appropriate focus items.
3: You may create an advantage with magic, using Will, Fight, or Shoot - though Will is limited to personal range aspects, Fight is limited to the zone you're in, and Shoot is generally limited to offensive effects - though subject to GM discretion; a wall of fire might be acceptable, for example, as it's thematically pretty similar to using a gun for a "covering fire" type of aspect.  As with ranged attacks, create an advantage takes a -1 penalty for each zone of range - again, this can be offset with appropriate focus items.
4: You may use "weapons" and "armor" in the form of focus items - for example, a really well-made wizard's staff might make all your magical attacks count as weapon rating four with an extra +4 to offset range penalties, or a blasting rod might allow fire attacks at weapon: 3 with +3 to offset range penalties, while a heavily enchanted leather duster might provide armor three, or a simple luck charm armor one.  Mundane authorities are unlikely to recognize the true nature of such implements, but anyone clued in is likely to be aware that a wizard with a staff is armed and dangerous, and lore rolls to detect their magical nature get a +1 bonus per point of weapon or armor rating they offer.

* * * * *

Now, someone like Dresden, a combat-focused wizard, probably has a number of stunts that add to this.  Things like:
Magical Thug: For the cost of a point of mental stress, you can make a magical attack that counts as weapon rating two... or +1 weapon rating over whatever focus you're using.
Reactive Shield: You've practiced to the point where you can raise a particular type of shield with a thought; you don't need an established aspect in order to defend yourself with Will.  (But you do still need appropriate justification - a force shield is unlikely to protect you from much in the way of social or mental attacks, for example.)
Focus, Focus, Focus: As long as you have an appropriate focus item in hand, you may use Will instead of Shoot for ranged attacks or create an advantage actions using magic.
Burn It All Down: +1 to any attack or create an advantage action using fire magic... but if you fail by two or more, the GM gets to place a scene aspect as the poorly controlled spell sets something else on fire.  And yes, the GM gets a free tag on that, too.

The catch is obviously Free Will - that's worth at least a +3.  So, you're protected from stuff like vampires, renfields (and any other human not acting of their own volition), and fae, and any denarians that have just overpowered their host and taken control.  But some random thug in a dark alley is a real threat, and mortal wizards would be especially dangerous.

Honestly, I'd just make this a -0 "power", that healing bite wounds is more difficult, and maybe move the +1 to track by scent thing over to be part of a "Echoes of the Beast" power.

Why?  Well, an actual serious bite wound is going to have to be a consequence.  And if you try to bite someone... well, yeah, they can take a consequence "bitten", but they can also take a consequence "sprained ankle" from dodging badly, or they can decide that this fight isn't really worth a consequence and try to negotiate a concession instead, or... etc.  So, it won't necessarily come up much - especially if your players follow standard player practice of never wanting to let an enemy get away.

And when it does come up... well, that's just an invoke of the consequence, or maybe a compel from the GM.  Not worth paying refresh for.

Yeah - this sort of thing should be extreme consequence or take-out territory (and I'd be rather hesitant to cut off someone's hand or the like with a take-out result unless either the player suggested it, or it was explicitly on the table at the start of the conflict - something like "Looks like someone framed you for a major theft; if the city guard gets a hold of you they're going to cut off a hand as punishment" - and then make very sure the player has plenty of options to concede - "I get captured, but my loyal crew will break me out, so I don't lose a hand, but have to flee the city," or "I miss the leap from rooftop to rooftop, break through a weak spot in the ground, and now have to find my way out of the sewer system... but the guards didn't get me," or etc.)

I'd strongly suggest taking a look at the Highway to Hell thread - it details a similarly city-less campaign, and is generally full of awesome.

Kind of expected to be attacked with fire. What actually happened (most recently) was 'slightly' different. No, instead of being attacked, the blasted Fallen I pounce (and poison, woo hoo!) is wearing some armor, that when penetrated, applies 'On Fire' at 9 shifts, which shortly there after burns off my wings (spell generated, think conjured biology, so only bad from the perspective of no longer flying), resulting in a flaming cat auguring into the bay.

Sounds like fun!

Sounds like, for most games, they should be in the same category as the fae Queens - they can do whatever is thematically appropriate for them to do, and tend to challenge the PCs to work around them instead of directly besting them.

Of course, I'm also aware that this doesn't really answer your question - and Sanctaphrax likes statting things that shouldn't normally have stats, so I'm sure he can help you there better than I could.