Those are all 6V servos. You need a BEC like THIS in order to power your RX and servos. That will allow you to convert the 8.4V from the Lipo to 6V for the RX and servos.
About the highest mAh rating you're going to find is about 1600mAh or so like THIS pack. Youll see some that claim to be 2000mAh but in my experience they arent really 2000mAh. Now if you can find room for it you can use a 6V NiMH pack like THIS that made from Sub C sized battery cells instead of...