2) Finally, if I was able to take an engine and take all the blades out (compressor & turbine etc), rotate them (90 deg?) so the engine would have to turn in the opposite direction, would it make any difference (obviously ignoring the effects of where gearboxes and the likes are located and airflow disturbance etc.)
I believe you meant (180 deg.) which is possible. This has happened in a single stage and the engine will still run, but fatigue usually sets in ala EAL DC8 out of New York many moons ago (does anybody have the famous photos of it burning on climbout).
Actually if you do manage to install the blades backwards (180 deg out) the inciodence angle will still be somewhat effective although the pressure rise/drop will be less.
comments/corrections welcomed.