Questions about landscapes

Hey!

So I just switched over from Unity to Unreal Engine but I am still pretty lost here about how to create a landscape that suits for the type of game that I am going to create.

I am going to create an open world game that is located in the wilderness far up north with lots of snow and mountains but still have different biomes like forest, oceans, snowland, iceland and other biomes but I don’t know how big my map should be. I want it to be big so there is much to explore and it doesn’t feel weird when walking over to another biome just a minute after arriving to one. So I want the map to be really big, but not randomized because I will still need to make villages and such things by myself.

So my questions are:
How big should my map be? (Please answer what to put in Unreal engine in the scale section)
How do I make chunks that loads whenever a player get’s near it?
What should the overall resolution be? (I want to make this game as pretty as possible)
How do I create realistic snow that is put over the terrain and mountains and such to make it look as realistic as possible?

That’s all my questions. You do not need to answer all of them by yourself, you could just leave tutorial links that is understandable for a beginner like me.

Thanks!