Terrain map size

Im new to using blender and was wondering about the terrain size and it I want a open world do I just create a massive single terrain that also includes the villages and any caves or do I use layers and create actions to take you to that layer then I reacha certain spot to help with memory?

If so how limited would the size of a game be with the layers?

thanks for any help

It doesnt really matter what size you make your terrain. The only issue you will be having with massive terrain size is with camera clipping in the blender 3d model viewer, that will be annoying. So for advice for a new guy id say, make your terrain not any bigger than you see the grid in the 3d view. Make the terrain small first, and once youve textured it, then scale it up to your character size. My character size I like to use is always 2 blender units high by 1 unit wide. Minecraft has those units too.

If you dont know how to start off making custom terrain, you can try going vertex by vertex and elevating extruding edge by edge until youve got something like this.

If im making a game kinda like skyrim that has caves and stuff do I just make those in the terrain too or make them seperate?

you would make those in a separate scene