That is a huge map, and looks pretty good so far.
For snow you could mix in some blue (or chooses a more bluish-white) and then add some clouds/noise or texture/pattern to it.
You could try putting a bit more blur on the area in the lower right, not sure if that will fix it or not.
Oceans - I think a darker color blue would work better (but that's more of a preference thing), same options here as with the snow (clouds/noise/texture). You might look at the Finished Maps forum find one that appeals to you and contact the artist to see how they did it.