Terrain Questions...

So I am looking at making a small open world environment. I am currently using World Machine 2 to create my terrain. What I am wondering is, what is the particular workflow I should use? I have seen tutorials where you can create your terrain and terrain textures inside World Machine so when you import it into UE4, you can make blended landscape materials that map to the terrain based on an alpha mask (I think it was an alpha mask, please correct me if I am wrong). Anyway, that is what I intend on doing.

However what I am not sure about is:

  1. In terms of Km, what is a good size for a small open world map, maybe 30km by 30km?

  2. What resolution should my terrain be, and is an 8K resolution overkill?

    • As it is I plan on using 4096 x 4096 resolution, but if 8K won’t be a potential performance killer, maybe I’ll use that.
  3. Should my landscape material resolution be the same as my terrain?

Edit: Also, should I consider using tiling to optimize the terrain? I mean I don’t want to remake a Skyrim size map, but still big enough to be considered open world.