You only 'need' 4 channels. The cannon and MG work off of the elevation channel (they work off an exponential signal generated when you flick the stick quickly to full elevation/depression).

Extra channels (more than 4) are nice to run lights or other gizmos, but the Persh lights don't need an extra channel. They are run off the turret channel via the dmd.

One of the best things I use for understanding radios and receivers is to get a cheap servo and 4.8v battery pack. That way, you can plug the battery into the receiver without it being in any vehicle, and move the servo from channel to channel. You can verify the rx works, and visually see just what the transmitter's sticks correspond to on the rx.

Fire buttons are very nice for battling, as they let you shoot on the move.