There are lots of different things you can do, but possibly the easiest if you happen to have an image of an old piece of parchment is to import that image onto a sheet that has a Blend Mode sheet effect on it set to multiply right at the bottom of the list of sheets (on top of everything else in the map).

I expect lots of others will come along and recommend more ways of doing it that are equally good, but that is one way of doing it within CC3.

That would work, but you have to get exactly the right one, and that's not easy.

If you use SIMPLIFY and tap in a nice small value when prompted (which is in map units and can be a fraction if you like), you can remove all the nodes that are closer than that distance together. Sometimes you might need to undo and try again with a smaller distance, but it should undo if you press CTRL+Z. Better save the file first, though, in case it doesn't.

EDIT: I've just thought! If you have a multipoly there you will need to explode it once first to break it into polygons and then re-multipoly it again afterwards.

I think it might be easier to just say that there is a dusting of snow and keep reminding players.

The default sun position in CC3 is from the north west. That's because most modern atlas maps with hill shading are shaded as if lit from the north west, even though the sun is only ever in that direction for real if you live in the southern hemisphere. The reason for this is that the human brain expects to see things as if shaded from 'above', as if the map is hung like a picture on a wall. It's easier for us to see the shape of those shaded hills.

That's just a lot of possibly quite useless information there, but it is the reason the default sun position is 315 degrees. I tend to leave it there unless there is a reason for changing it - dramatic effect, or some other reason.

But again - as Dalton says it really is a matter of personal preference.

If you are working on top view maps it's a question of shadows.

A spire would be either a circular roof or some regular polygon shape, so they can be drawn using the House tool with a roof texture of your choice, on a sheet above all the other building sheets in the map so the long shadows they cast will fall over everything else. Or you could pick from the City Domes annual issue https://www.profantasy.com/annual/2018/bonus18.html which contains all kinds of small regularly shaped rooftops that could top a tall tower.

A spire might have a tall pinnacle above that roof, so you might need another sheet above that one to draw simple very thin pointy shadows to suggest that the little 'bobble on top' of a roof is actually the pointy bit of the spire.