How much voltage do you want to run. If you want a good solid setup with decent speed and the abililty to run on a track, then a two cell lipo pack will do you. How much runtime do you want? Since you already ordered the hyperion charger, I'd also get the hyperion balancer (lba10) to go with it. It's a solid setup and will take good care of your batteries. Just be sure to get the link that goes between the charger and balancer. A good economy battery would be a maxamps 5000mAh 2S pack. If you want more runtime, at the expense of weight, then the 2S2P 8000mAh pack would be nice. Get on the maxamps website to check the dimensions of the packs to be sure that they will fit. The maxamps packs also come standard with hyperion compatible balancing taps.

I balance charge my batteries every time I charge them. Not so much because my packs need balancing, as much as it is because the balancer can also detect problems with the packs, perhaps crash damage that wasn't visible to the eye.

If you haven't already ordered the MM setup, do your research. My favorite setup is the 4600. I like it because it is so flexible. It makes a nice controllable track motor on 2S lipo. Faster on 3S and insane on 4S. The 5700 is the next best. Fast on 2S, insane on 3S, although not quite as insane as the 4600 on 4S.