Can I drive my car without...
 

the radio, climate control unit, window/PSE/top/lock/defrost switches installed?

If I pull these out to work on them and it takes a while (or God forbid, I screw something up) can I drive my care without messing up the computer/security/etc if these things aren't installed?

I'm guessing I'll have to have the instrument cluster installed :)

Except for the PSE switch (I don't have one), this is how I drove my 2001 S for a week while repainting the interior trim a couple of weeks ago. I didn't even have the center console installed.
I only re-connected the top and window switches in case I needed them, everything else was disconnected. You'll just need your radio code when re-connecting the radio (assuming you have a Becker).

Should be fine. PSE should default to "off" as usual.

I don't have any of these switches in my Spec Boxster race car and everything is fine with the stock ECU and immobilizer.