One technique to rule them all?

Pre-shading of panel lines can be disappointing on dark finishes- it works best with lighter finishes.  For dark paint, a pinwash may work better for panel lines- a slightly different look, but more realistic for these darker colors.

I don't find scale makes much difference.  Color of paint, the type of weathering you are trying to depict, are more important.  And bare metal finishes are considerably different for weathering and other effects.

Thanks Don.  Its all quite overwhelming, especially when half the plane is dark and the other half is light.  However, I see your point with dark paint underlayment.  Thank you for your help!

If this were me, I would start with a layer of the callout color.  I would next highlight between panels using a pale shade.  I prefer a tan for brown or green, greys for a blue, or that callout color mixed with a bit of white, maybe 40 or 50 percent.  Then I would lightly cover with a very thin layer of callout color,  just until the highlight shows but is no longer defined.  Then a pin wash of panel lines.  That would be my 2 cents, for what it is worth.

As Don suggests, the scale doesn't really make much difference in most cases. Though if doing mottling, you may have to adjust how you use your airbrush. The spots on a 32nd aircraft will look out of place on a 72nd. Thinner ratio's and pressure may also need to be adjusted.

I use the same methods on what ever the scheme I am doing, the only thing I adjust is the colour I am using for weathering, dependant on the colour I am putting it on, and how heavy the weathering is dependant on what result I want.

Thank you guys. I really appreciate the help. I'd like to try the method of fading the panels Andrew but my airbrush skills need much improving! I saw a great BF 110 build article utilizing that method and the final product looked absolutely superb. I'll definitely give it a go once I'm more confident in my technical ability!