Welcome to ASC.
First thing I would recommend.
Get Age Verified, This will allow you acess to the Classifieds, AV'ed Retailers, and Age of Majority threads.
Next check out your local area, see what people are using, and just get your feet wet before you leap right in.
Finally... I would not reccomend a Sniper Rifle as a starting wepon, AEGs all the way.