Gday Mr Meadows
For your first efforts, I'd say you have dived into the deep end! But that said, you are showing a creative eye for the diorama...
Going to the effort of realistic backgrounds and some b/w imaging shows that you know what you want out of your dios...
As the others have said it is kinda hard to give an honest critique with the images as they are... How about breaking down to the basics, with just the base AFVs and figures featured, in colour?
There are some stellar dio makers on site here, and for your next project (There are going to be plenty from you, right:) ) you can get the input you require from initial stages of layout ideas right through to what colour window panes for that period...etc...
Keep 'em going
Cheers
Brad