Bluemoon,
you'll see from some of the masterpieces on this site that there are various ways of doing shadings/ gradients. the main thing is to determine the shape first - some aircraft actually have curves in unusual places. Being a PS guy, I usually incorporate a fuselage gradient within the first skin - then I darken the other/ outer areas using a combination of large and smaller soft brushes. If the shading looks too dark - reduce the opacity. Warning - my experience is that the shading always comes out darker in the printed product. as to the bare metal thing - i'll let someone else answer that - there are some good examples out there. HTH,
Michael