1.  As already mentioned the White Court should probably be the leading faction.  Vegas is the city where emotions run high.  All emotions.  It's easily the best White Court feeding ground ever.  It'd be interesting to have more benevolent White Court members too, since Vegas is a perfect place to "sip," such as Thomas does later in the series.   

2. Vegas is also a drug haven.  Red Court should definitely have a presence.  But I'd put them as the leaders of the more underground aspects of Vegas.  I.E running the casino's the tourists don't visit.  Gambling with both mortals and supernaturals a like.  Trying to make lots of money both legally and illegally to help fund the war they all know is coming eventually.

3. Vegas seems like the perfect place for Tessa to hang out in her off seasons.  She likes recruiting the desperate and Vegas has no shortage of semi-wealthy men and women who bet their whole life savings on their last good hand or roll and lose it all.  How are they going to go home to their spouse and tell them what happened?  What are they going to do to support their kids?  Along comes Tessa offering them a chance out.

4.  I'd definitely consider running the campaign there without Wizards.  Sorcerers, maybe, but WC wizards just have too much of an effect on technology and most of the casinos and hotels there are lined with technology.  But it's a perfect place, if your campaign allows it, to call on help from outside using Harry and Elaine's network.  I can definitely see Wizard NPC's coming in to help on some cases, but I just can't see a wizard LIVING there or even operating there regularly.  Seems like a great place for wereforms and vampires though.  All the supernatural weirdness can be explained by tricks of neon lights and witness' drug abuse.

Just my two cents:

You should look at the lore of Dresdenverse in general, since that is what this RPG is meant to emulate.  And if you do you'll find fully Fae characters don't have the same free will mortals or changelings do.  When Harry interacts with Lily and Fix after they become Summer Lady and Knight, they are literally not allowed to help him directly.  They're not allowed to fight with him, and they're not allowed to give information to him.  Even though they WANT TO.  That is pretty much the definition of NOT HAVING A FREE WILL. 

So in game, like all games of this nature, it's entirely up to the GM if he/she wants to allow it, but as far as the lore of the novels go, and the rules suggested by game designers, a fully Fae PC isn't possible.