About motors, for a power to weight ratio the astroflights are incredible, but so is the price. If you can afford them, go for it, but also make sure you can afford to lose one in a battle. No sense in making a robot with expensive materials, and not being able to afford replacement parts.

About the batteries:

SLA can blow, nicads can blow, Nimh can blow, Lipo and Li-ion are no different. The material gets lighter, the fires more spectaculair, thats all.