Removing P/S pump, sealing rack...

I believe you have to put a loop hose between the two ports. Fluid will want to move back and forth as you turn the steering wheel. Just draining all of the fluid probably isn't a good idea since the seals and stuff will dry out.

Is it a good idea? Go outside and try to try the steering wheel when the engine isn't running. You be the judge.
 
Not a good idea.

If you want manual steering, you need a manual rack. Using the Power rack without fluid will cause to eventually fail....hopefully not while you are driving