[MetalMan]

The Orion packs will work. In my mind, the problem with having a hard case on a Lipo is that if it were to puff up, you wouldn't know it. Then, the plastic case could explode from the internal pressure, spreading hot plastic shrapnel. But, they are more than enough in terms of amp handling capability.

For an E-Maxx like that, you would only need about 45amps continuously rated batteries. There are many choices out there, and usually (for me anyways) the budget is the limit.

Charging Lipos is much different than NiMh. They charge using CC/CV, which stands for constant current/constant voltage. This means that for most of the charge, the battery will be receiving the full number of amps (constantly) that you set the charger to charge at. Once 4.20v is hit, then the charger goes into constant voltage mode, where the battery is kept at 4.20v (per cell) and the charge rate tapers down.
Balancers keep a pack in good shape by equalizing the voltage of each cell at the end of a charge. There are many balancers out there, and some work differently from others. Hyperion makes one that goes between the charger and the battery, but usually the balancer is connected externally from the battery through things called "taps". Taps are external points for access to each individual cell. A standard balancer (unlike Hyperion's) will connect to these taps and basically discharge the cells until they have the same voltage (it will discharge the higher voltage cells).

Hope that just about covers it :).