Futaba doesn't give a specific maximum current draw for your servo, but they can exceed 1A when under maximum load. Running four or five of these servos should not cause damage to your receiver. Usually, an isolator would be needed if you are running more than two servos from a single channel, and that's because of signal degradation.

You should be able 5 of these servos with the battery pack and servos all directly connected to the receiver.