1.) Can't say for sure they'll be thier since I don't work for EE, but as far as I know they plan on it, and their have been Warzone tournaments at the last several Gencons If only I didn't live on the wrong side of the country I would have got a chance to play.
2.) pt Size depends on the event and what the event organizer has planned.
3.) They're all about equally common, though I don't hear about too many armies from the tribes of earth.
4.) Get the rule book. Its got the complete army lists for every force as well as tons of fluff, after that pick one you like because they all have similar learning curves, and after that its just about style and preference.
Put up a post in the player locator, somebody near you might be starting up a game and need players, that way they can at least send you a PM.
Lastly welcome to the forum!