RE: 4.8v vs. 6v receiver batteries
I'd keep the 6V pack. It will make the servo's produce more torque and they will respond faster. A charger for the 6V is at Tower Hobbies for $69.99. This is a great charger and will charge two batteries at a time. Hope you stay with the 6V you will like it better than the 4.8.
Gibbs