The Story Untold ... So Far

I have a story in my head.  A HUGE effing story! If I put the whole thing out there, I think it would be a book, a large-ish book, even. 

I have written pages and pages of character bios and outlines. I know the world, the society, what will happen and why. I even have a whole entire folder on Lappy for the chapters.

Problem is, I havent written the first word of chapter 1. I am absolutely paralyzed with fear.

• I am afraid that I have no idea what I'm doing - and I dont. I have read a lot of books, but written VERY little. 
• I am worried that the story will become unweildy and get away from me
• I am afraid that what I want to write will just not work
• I am afraid that I will change my mind on exactly what I want to write and how I want to present it and have to gut the whole thing - rewrite a bunch of shit
• I am afraid that it will be embarrassingly lame and suckie

So?  I do nothing.  I set up everything in early October.  Havent done a single thing with it since.  I have no excuse.  It isnt like I am busy.

What the hell do I do now?  Shit.