Looks really good, you have done a good job with the partial snow covering.. The snow suits look good, but the helmets stand out a bit, they look to 'plasticy' to me..try giving them a coat of diluted matt white, to break then up a bit. Other than that ( and the sprocket and idler...

) It looks good.
Both the Marder on it's own and the dio as a whole.
I believe it's o.k. to show an entry for a campaign on a dio, even if the dio is not part of the entry. I hope so as that's what I did with my Tank Terror entry.....
Cheers
Henk