What they said! ( I see the usual suspects are here
)
I really appreciate the 'swappability' of the model. That way should make it easier to produce multiple versions indeed.
I am by no means an accomplished modeler but there are some things that I have learned over time that might help you in some way.
Concerning the mapping of the mesh: if you start unwrapping the biggest version (longest wings, biggest empennage and cowling) and plot that mesh on a texture sheet, you can be assured that the other versions will also fit on the same texture. Theoretically, you'd then only have to remap the 'interchangeable' parts and unwrap them to the relevant spaces on your texture sheet. I am sure you have already thought this out but if there's one thing I have learned is that careful planning can save you a lot of time later on. Unfortunately, my eagerness to see things come to life has forced me to redo a lot of stuff over time. Patience can be a virtue...
This also goes for the size of the gmax UVW map: There are some tutorials around that teach that size does matter. They calculate what the size the UVW map in gmax needs to be by the size of the rivet you want to paint on your texture (eg. 6x6 pixels) and the size of the .dds texture sheet itself (eg. 2048x2048 pixels). This applies not only to the external model (you'd want the main parts of the model on a single texture sheet if you wish to use a .mos file to show damage) but also for the VC. Although it seems you can have as much texture sheet for the VC as you like, the number naturally taxes you PC. I didn't plan this very well for the VC and I now have a lot of textures for this part of the model.
Even though CFS3 doesn't support PBR there's a lot you can accomplish with the gmax material settings and the use of _s, _r and +nm texture sheets. Again, planning is key here. To make life in gmax easier I would now unwrap similar materials to the same texture sheet(s) as much as possible: Eg, bare metal VC parts together on a sheet, painted parts on another sheet etc. All depending of course of how detailed your 3D model is (number of parts) and what resolution you're after. Next time I would also try to reduce the number of multi-materials in gmax as much as possible anyway.
However, if the 'swappability' of your model also applies to your VC (different instruments, throttle lever styles, gunsight types etc. for each Mk.), it would be convenient to keep those interchangeable parts on a seperate texture sheet and leave the 'generic' parts on their respective sheets. This way you can keep the number of texture files that need to be changed with each variant down - less textures, less strain on your PC!
These are just a few things that leap to mind. Other than that, download Tom's (Hairyspin's) tutorials on unwrapping. They can be of great use when it comes to unwrapping those really awkwardly shaped parts! Oh, I do have found a setting for perspex that I find quite convincing in CF3, so if you need it...
I'll be following your thread with interest, so keep us posted!
). Right now I'm intending to start by producing the Mk Vc as it's a variant I've yet to see done to a highly accurate standard. 
