Number one... did they also give you a battery? If so, what brand/model is it? If they didn't give you one, I would suggest you buying a pair (at least) of Samsung 25R (green), LG HE2 (red), or any of the other "good" batteries out there from Samsung, LG, or Sony. There are other good ones, but those are the ones I trust.
As for tanks, a perfect starter, that will grow with you will be the Kanger Subtank Mini or Toptank mini... they're the same tank, but the top-tank can be refilled without removing it from the box-mod