The preferred setup seems to be a 17 tooth pinion with a 3S3P LiPo pack. Some prefer the extra flight time from the 3S4P at the expense of a little added weight.
For the battery try Thunder Powers own website. The pinions are easily found at any shop that sells Traxxas E-maxx truck parts. The pinion for the E-maxx is the same as the pinion for the VE.