Is it possible that the computer also checks the pressure in the pumps of the harnesses before each launch? Or is that something that doesn't need to be checked?
No, you are the hydraulic pump for the restraints (see my most recent post in the "Restraints" thread). And the bar is locked when power is not applied. So really the only thing to check is a limit switch to make sure the bar is down to an acceptable level. Assuming they even bother to do that much (Millennium Force, for example, doesn't!)
--Dave Althoff, Jr.
Could they theoretically alternate the cars to be more of a face-off type of arrangement?
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In theory (and some electrical reworking as described by Dave) yes, but I wouldn't want to be facing backwards during the launch.
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In physics class last week we were doing a problem on G-forces and the subject was being exerted about a 9-G force and my professer said he hopes the it was "9-G Eyes In", because he said if you have too many G's in the opposite direction, your eyes can pop out.