So I'm a ST who has a fair amount of experience with running other systems, but am pretty new to the Dresden Files / Fate system and I have a couple of questions about it.

1:  The Character Creation chapter stresses that a template is critical, why?  If someone wants to play something that doesn't fit in any of the existing templates, why shouldn't they just be able to choose what powers best represent their ideas, choose a fitting High Concept and be good?

2:  If you can grow from one template to another (Focused Practitioner -> Sorcerer -> Wizard)  why bother to separate them at all?  I guess that it helps to establish guidelines, but seems somewhat arbitrary.

3: I guess what I'm really coming down to is I'm considering throwing away templates as restricting what things people can take and using them simply as a starting point (the average X will have Y and Z).  Is this use as intended or does this break something?  I'm not quite sure why templates are important, and don't want to mess something up due to ignorance.

4: The City Creation section says to come up with faces for Themes, Threats and Locations, including their motivations and aspects as a part of group character/city gen.  How much of this stuff should be secret from the players?  I will admit my group hasn't done anything like the city creation before, so the way I'm handling it is to come up with 2 themes and half a dozen faces to hang the pre-written parts of my plot on and then incorporate what the players and I come up with, but I'm trying to figure out how much info the players should be given out of character about the motivations of X, or the reason that Creepy place Y is the way it is. 

Any advice would be helpful.  (Alternately any advice for someone new to the Dresden System in general).