Since I don’t know any of the pieces and materials the game comes with, I’ll have to rely on you to figure out if we have it all or not.
About scan size, the only importance is that the size of the map/board and pieces/cards/other stuff are in some way consistent enough with each other. Like, a miniature fits comfortably within a hex, without being bigger than it, or far too small.
The size of all the materials beyond this is of no concern in vassal, save for maybe memory saving and file size. But vassal can zoom in/out of the game area, making it all just as visible as it needs to be.
I can re size things on this end in Photoshop if needed too, so you can just send me what you’ve got so far and I’ll see about handling the rest.
I’m on Skype.