Oh well my 3 and a half cents worth Sure good comments, maybe like to add the following observations.
Shep Paine is seen as the master of what can be achieved, some of his dioramas have the wooden surround above the groundwork and did some amazing work painting crappy plastic Joe Blogg standard figures. Me I would say, why bow down to what is fashion, hone your figure painting skills and you will be able to make a crap figure look good. Obviously plastic figures can be enhanced by resin heads and hands, plenty of literature out there on how to further enhance plastic figure detail ie use a sharp blade to underscore webbing, pockets, jackets etc etc. Just look at the amazing results achieved by those that model Historex plastic figures.
Sure, purchase resin if you cannot afford the time to hone skills, if you have time it sure is rewarding to have a group of, say miniart figures that are not quite the same as other peoples. Just imagine how you can personalize your own miniature population in a diorama. At least with plastic figures, if you muck them up you won't fell as bad as mucking up a resin figure. Nothing like hacking and chopping plastic figures, plenty of putty etc and wallah, another masterpiece to be undercoated and painted. Just look what can be achieved on this site.
Your diorama looks great, thank you so much for sharing. If you enjoyed making it, way too cool, way to go. Having fun is the bottom line. Power to your painbrush.
Well! time for a deep breath, razor saw out, super glue ready, light on, coffee made so lets get to it.