well, you can start by getting some figures relative to what you're building, like U.S. WWII artillery men in this case. also look around for those that have interesting or similar poses to ones you are thinking of. even if they're not of the same unit, you can convert them.
to convert figs, use a razor saw to start cutting apart the various body parts. you need to reshape them for what you need. for example, cut an arm in half at the elbow joint. when you're cutting think of how the arms going to be bent. you can try cutting a wedge out to help bend the arm more. or just sand the ends of the bisected arm at the correct angles, to make the arm bend the way you want it. then simply reglue the ends where they join. but, if you're trying to straighten out the arm, or just bend it, dont try to fill up the whole gap you made with glue. glue the parts where they meet, and later, once they're dry come bakc and ust some putty to reform the missing or misshapen areas. you can use putty on other areas as well, like to reform or give a new shape to parts, without having to cut them, like adding pockets, or reshape a figurews neck to make it look like he's turning his head. you can cut off the hands, and drill out the ends of the arms, and then reglue the hands back on, to make it look like the figure is wearing a separate coat.
other people can probably add some more. they'll be along don't worry.
hope it helps!