Check the Tips and Tutorials at freeflightdesign.com. I've found them very
helpful (and even written a few). Many are step-by-step.
Also, gmaxsupport.com is another excellent site.
Concerning the transparent lower half: Do you have both reflective surfaces
and landing lights on your model? I recall reading that the presence of both
can cause this transparency. Try exporting the plane without the lights and see
if the reflective surface is ok.
Hope this helps.
Dennis S, FSEngEd@aol.com