I have the Micro Mark PE kit. I haven't used it yet to etch any parts. I created some artwork to do the etching. You will have to have extensive knowledge using a vector based design program like Adobe Illustrator, Corel Draw or Inkscape. Inkscape is free, you can download it here: http://www.inkscape.org/download/?lang=en
The reason you have to draw the artwork in vector is due to the fact that bitmap (jpg) artwork is blured on the edges and won't give you a sharp etch.
Micro Mark's website states the "Maximum overall size of etched sheet: 3 inches square x .010 inch thick."
If you want to do larger peices you should look at Fry's Electronics. They have larger photo etch kits to do large curcit boards.
Have you tried Woodland Senic? They have materials to do scenes.
http://www.woodlandscenics.com/