When doing a full Fate Core conversion, I wouldn't bother with elements any more. That's a thing for aspects now.
You are mentioning focus items a few times, yet you don't say what they are actually supposed to do. I wouldn't really bother with them, to be honest. Maybe make them a weapon instead, so when you are shooting magic with a focus item, it is similar to a gun. Or a focus item can be a stunt, for example a permanent justification to roll will for physical defense with a shield bracelet. Like your reactive shield, only without rolling to put an aspect up. The stunt pretty much is the aspect.
Thaumaturgy, to me, is very off the way you describe it. Since it isn't really a skill so much as a series of actions (not in the "the four actions sense, but a "first you do this, then that and so forth") you take, it can be a lot of different things, depending on what you want to do with it. It can be a simple overcome action, a contest, a challenge, or it may even become a full scene with a conflict and everything.
You want to open a lock? That's an overcome action.
You want to do a tracking spell? That's a chase, just with magic against athletics instead of athletics against athletics.
And so forth.
The ward you describe, to me, seems pretty boring. If the ward is never used, there is no need for it to even exist. If the ward is used, then someone is trying to get into your house, it is interesting, it is exciting, play it out. There is a "security specialist" stunt for burglary, that lets you get into active opposition if someone is trying to overcome a security system you installed. Why not do the same thing here? Just have an aspect like "this place is warded", and when someone is trying to get through, you make it a conflict wizard against intruder on the basis that so long as the wizard wins, the ward holds up.
And before you get into casting the spell and playing out what you do, you can prepare, create advantages that you might need. Some might even be required to just be able to do the spell. Like a symbolic link.
My biggest concern with all of this is that it really takes away the drama of spellcasting we see in the novels, which I think the current system handles nicely.
Really? I think the magic system in DFRPG is pretty clunky. You can still get a lot of drama here with success at a cost and the occasional compel, and those aren't just random things then, they'll mean something.