Broad concepts- Motor pwm and multiple servo control over xbee

I need help understanding some concepts about wireless using xbee and using multiple "simultaneous" outputs.

My proposed project: Build an rc model aircraft carrier with a variety of working parts.

For remote control I am considering using xbee. What I want is the ability to control multiple outputs (mostly servos) for things like elevators (4), ramps (4), catapults (4), crane, anchor, bow thruster (reversible motor), several different lighting schemes, and others that maybe I would add as the project progresses. I am thinking I would put an arduino mega on the boat since as I understand there are up to 48 outputs. I could also have a mega on the transmitter end to handle all the switches and buttons. What I don't know: it is possible to control 20+ outputs wirelessly. I understand xbee has 8 digital outputs. Does this mean that I could effectively only have 8 "channels" (if digital pin 0 on the transmitting xbee is set high then the receiving pin 10 on the mega for example is set high) Or is there a way (multiplexing?) to say if pins 0 and 1 on xbee are high then, for example, pin 21 on the receiving mega is set high, and if pins 0 and 2 on the xbee are high then activate pin 22 on the mega, etc. Or does it not work that way?

My second question has to do with operating these devices while running the motors (I have the motors hooked up to an H-bridge I made and am controlling with PWM). Obviously I would want the portside and starboard motors along with the rudder servo to have priority. And it is not like all of the servos would operate at the same time. In reality, probably only 1-2 would be operating at any one time. But, for example, I would like to be able to keep the motors at a constant speed and control the rudder (to keep the deck into the wind) while firing the catapult to launch the plane. It seems like operating one of the peripheral devices might interfere with the motors or rudder or would the few milliseconds to set a pin high not really be noticeable?

Thank you for any suggestions or assistance in helping to understand these concepts.

What I don't know: it is possible to control 20+ outputs wirelessly.

Yes.

I understand xbee has 8 digital outputs.

If you use them, yes. You don't need to, since the XBee is going to be on an Arduino which has more than 8 inputs/outputs.

You can send something like "<S,42,1>" to turn pin 42 on or "<R, 29>" to read pin 29. The receiving Arduino then needs to parse the data and perform the requested action.

It seems like operating one of the peripheral devices might interfere with the motors or rudder or would the few milliseconds to set a pin high not really be noticeable?

You misspelled nanoseconds. PWM or servo control is not suspended while you set a pin HIGH or LOW. That stuff keeps happening, based on timers that tick away without your knowledge or active participation.