Where the second stage meets the first stage is presently just a visible geometry line, but I've just now done that line as an actual seam. As such it could show up in some shots (when rendered) and not in others depending on how the light falls on it. I'll do the same for the separation between the second stage meets the third as well as the access door since otherwise it would be totally invisible given it's the same silver colour as the majority of the hull. The windows will be done as slightly transparent pale yellow and I think I'll add a rudimentary interior. I haven't mastered lighting yet in Sketchup but I can try to add some illumination to the interior to show the windows off more.
The exhaust nozzles shouldn't be too hard since I really only have to make one and then duplicate several times. Colour is largely conjecture since the film was b&w and the only colour reference on the drawings are that most of the hull is silver and we can infer part of it is black or dark grey.
When I'm done I want to do some Photoshops of the ship going into space.