Got mentioned before but bears repeating: Everyone wants different things from a game. Unfortunately this too often gets paired with something a bit like one of the annoying internet memes. "If you're not doing it my way, you're doing it wrong." A common enough sentiment and easy to fall into but decidedly false.

If you fall into a group of people that want a lot of the same things you do out of a game... Great! You've gotten VERY lucky. If you're like the majority of gamers and haven't been quite so lucky, what you get out of a game will largely depend on the approach you and the rest of the group take towards acknowledging your differences and meeting in the middle. You'll have to avoid hopping on a soapbox while you do this and don't let anyone else get overly comfortable up there either. That won't help any. Just figure out what you enjoy, what makes you happy in a game and see if the group and the GM are comfortable working that into the experience.

However the initial talk goes, you'll also have to realize it's going to perpetually be a work in progress. You can't just do it right once and then drop the idea. It's going to always be a compromise, but there are many different ways to do it. Rather than every story being directly in the middle of everyone's comfort zone you might find the players who are more into storytelling are willing to go for a more crunchy, combative storyline as long as the group is willing to accommodate them later on.

One last comment, going with canon can sometimes be it's own argument. It's also one an author doesn't run into to the same extent that a group of gamers will. If they want to add something to their canon they only have to worry about it breaking their own previous ideas rather than being concerned that it might mess up someone else's character.

What is possibly a more interesting and useful way to look at this for NPC's in general would be "How much influence does this mortal PC have with this supernatural NPC?" I think there are a number of examples in the novels where a normal mortal got a supernatural to adjust their thinking a little in response

You are totally free to adjust how free will works in your game. I don't think there's any One True Way to handle the topic. But the default assumption of the world setting is going to be that supernaturals don't gain free will. To alter that you'd have to either insert it as a basic premise or add it as a consequence of a storyline (and since it's a central-ish theme it would probably need to be a pretty epic storyline).

For Items of Power it might be easier to think of it from the story point of view rather than the system. People who wield an item of power become known for it. Michael in the early novels isn't just Michael. He's Michael-who-wields-a-sword-of-the-cross. You know as a reader that anything involving him will involve a sword of the cross.

This isn't true later on when someone else picks one up and briefly swings it around.

The line is fuzzy but when it's crossed, that's when someone should pick up an appropriate Aspect and lose the Pure Mortal bonus. Batman for example isn't famous for his gadgets outside of internet memes ("bat shark repellent" is a joke, not something we seriously expect him to produce on demand in another series).

As for the loup garou... I would say that's just a subset of something more general that holds true in all RPGs. Which is simply that some enemies are setup in a way that not all groups can handle equally well. Anytime you get into specialized attacks and defenses or go higher up the power scale of the system this can get more pronounced.

I'm not certain what role that's supposed to play without some context. Looks like it's designed so some info is easily visible to the rest of the table while other parts are less so? Wouldn't say it's exactly hidden as anyone sitting right next to you could still easily glance over.

I don't think you'd need to change much. Just remove the homeworld part and put in a spot for powers. Probably easiest to do by hand and then photocopy it.

I haven't... but if you want random ideas from the peanut gallery feel free to ask?   World creation is fun.

I love the Amber Diceless system. Had quite a bit of fun with it. If I had to explain Fate to someone who'd only played Amber and D&D I think I'd compare it more to Amber.

Your character's skills are a lot like Amber attributes broken down into more specific areas. D&D style attributes are basically not present in either of the other systems.

Aspects and Fate points are a lot like Stuff in Amber. Like skills, Aspects are broken down a bit more than their Amber equivalent. You have multiple Aspects and because the world setting for the Dresden Files is more about gray areas than Amber is, the best Aspects can be looked at in both a positive and a negative light, like the "barbarian" example above. So Aspects handle whether you have positive or negative Stuff, while Fate points are the actual measure of it. The usual style for gameplay is to complicate the life of the characters by drawing on or "compelling" Aspects in a negative way and both the GM and players can get involved in that (subject to GM approval of course). Then when the plot comes to a climax you have resources to burn.

One important note about Aspects is that they're all over. They're basicall soundbyte sized descriptions of what something is, what it's tied to, etc. In Amber you're encouraged to add details to your surroundings subject to GM approval. In the DFRPG you do the same thing by declaring an Aspect but there are rolls involved. This may feel a little complex at first but mostly as a player you should just keep in mind that you should just keep in mind that like in Amber you're a lot better off interacting and taking a role in the narrative of the story than just hiding behind numbers.

Powers are actually very similar to powers in Amber. Stunts are a bit like having a rank in an Amber attribute. You're good enough with one area of a skill that it requires special description.

The rest past that is details. You'll have to decide how much nuts and bolts you want them to handle and how much you're willing to smooth over in the first few games to get the ball rolling. Fate has some really wonderful ideas. To be honest, as much as I like Amber, if I ran it again I'd be incorporating some of the ideas I've seen in Fate and the DFRPG. But the downside of that is that they're new ideas. I don't think it's really possible at this point to start a new group in Fate without handling a lot of the mechanics for them. Must see if Fred has a World Conquest fund going or something.

For a side story with a bunch of players who like story, I'd kind of lean towards a hag or a witch type of villain. Something magical and dark that's latched onto those particular children and wants to make kiddie stew and crunch their bones. Make the bad guy really tough if you like the idea so it can come back later.

The twist is the kids aren't entirely defenseless. A pixie has gotten attracted to mess and is busy playing faerie godmother and protector to one or more of the kids. The pixie isn't going to be able to keep it up though, he/she is depending on trickery and misdirection mostly. The pixie's motive is it's a flighty critter and this seemed like a good idea at the time. Adds a motive to the bad guy as well. It's recently heard of the pressed fairies book and the pixie has annoyed it enough that it wants to make one.