Hey, cool Wookiees, Fritzkrieg.
So, did they kill all the Clones, or are they coming upon the Clones after the fact?
Looks like you're on your way.
One suggestion - and it's a tough thing to do, so don't worry too much about it.
Insert a layer between the background and all your pasted in figures. On that layer, use your airbriush to paint shadows on the ground under your figures (figure out where your light source is, then paint accordingly). It's OK if they come out too heavy for now. Black is even OK so long as you have faded edges.
Next, tone down the opacity of the layer with the shadows until they look about right. You might end up going all the way down to 10% or less. Opacity is an option on my version of Photoshop on the Layers pane... I'm not sure what you might be using, and my version is really old, so...
This may or may not be too much to worry with right now. It's one of the reasons I hesitate to use full-length shots of figures; I hate worrying about marrying them to the ground with shadows. The good news is that once you get in the habit of doing this and you get your own technique down, it will be something you can add on with little to no worry.
This really is an impressive first effort. You're well on your way to churning out some really cool stuff.