Of course you can map multiple meshes on one image. Instead of creating a new image for every mesh, you can also select the same image, you already used for another mesh. For example "fuselage.jpg" in your screenshot could also be used for the wings if you have enough space left on that image.
Look at the picture:
OuterWing_Left and Pylon_Inner_Left are 2 seperate meshes, but are on the same texture-image called SimplePlane_LeftWing.jpg
You have to export the UV-layout for every mesh, insert it on your texture-file, save it and then reassign it as texture for a mesh, so the changes become visible. I think it's not possible to just view the mapping of all meshes together at once, because you need to be in edit-mode to see the mapping and that only works for single meshes.
The general way (for me) is:
- create a the texture-image in Photoshop.
- map a mesh and select the image in blender as texture-file
- place the mesh and export the uv layout (UV/Image Editor"-windows menubar "UV->Export UV Layout")
- import the created .png-file with the meshlayout as new layer to the texture-file in photoshop (important: insert to original position, otherwise it is placed on a different position on the texture-file than the actual mesh is)
- save the updated texture-file
- reassign the updated texture-file on blender to see the meshes, that are already mapped
- repeat until done
That way, you also create the base for your models skintemplate.
You should have something like this, if you have finished mapping all single meshes of a model: