Since we must begin somewhere lets begin with what we do know about the Syldavian military. Sadly in this exercise we are not blessed with a wealth of source material. In the book there are a total of three images depicting Syldavian soldiers. The image below is one of the clearest images of (presumably) an enlisted soldier and officer.
In this and the few other images an image of the uniform and appearance can be wheedled out.
1) Helmet (this appears to be a Swiss Model 1918/66 helmet)
2) Coat/jacket. Presumably wool with two or more pockets, a stand-up collar and closed with four+ buttons (silver in colour).
4) Trousers, straight leg, wool.
4) Boots. These appear to be of a “pull on” variety, not unlike contemporary German marching boots. As for their colour they could be either black or brown (soldiers in dress uniforms are depicted with brown boots).
5) Insignia/medals (Only depicted on officers)
B. Breast, left. Service medals?
6) Belt, black or brown (officers are depicted wearing “Sam Browne” style belts)
7) Rifle/side arm. Presumed but not depicted, although the police are shown with what appear to be bolt-action rifles.