Yeah the minimum you need for a weapon is 3ch. Drumroll's drum is on Ch3, if I had a self-righting arm on it, it would be on Ch4.
Personally I find Ch5 to be a bit restrictive for some weapons as the switches tend to be On-Off, or fwd-bck with no middle ground. Obviously you could replace this with an On-Off-On switch or an adjustable dial if you wanted to but that's hassle :P
I know some spinners use the switch if the weapon is just relay-controlled, but for electric axes/lifters, I would find it much more flexible and controllable on a stick channel. What do flippers tend to use? Can you just get by with flicking the switch on to activate the valve and then rely on the elastic to retract the flipper plate?