Hi there VonBarb. I'm pleased you like the screenies. Here are a couple of raw screenshots before editing.
Generally, I use the screenshot as a background layer, right at the bottom of the layer stack. On top of that I put a white fill "paper" layer with the opacity lowered so I can see the screenshot beneath. Then the process involves working on groups of layers to deal with the various components of the picture. The background and internals/cockpit tend to come towards the bottom of the layer stack, the fusilage in the middle and the foreground and shade/highlights on top.
I use the pen tool and "make selection" to create the various shapes based on the screenshot and then fill them with either the paintbucket tool or the gradient tool. Finally, I bring the "paper" layer back up to full capacity and flatten it all.
Thanks for looking Nico and happy simming.