1920 polish uniform colors

Hi, I’m thinking of adding a few figures to my Austin armored car. I have one polish soldier and wanted to add a few more. First question is, would WWII 1939 polish figures work? Second, the uniforms appear to be imperial German uniforms, am i wrong or right in this assumption? Third, what color should i paint them, is it field gray or more of a Russian khaki green/ brown wool?