Optimal Texture Resolution for Saving Texture Painted Terrains?

I have remade the intro map of Silent Hill 2. The terrain size is 1 and a half of a football stadium.

I think I would go for an 8000 x 8000. Is that too small or too much? Will it cause blurry textures?

If seen from a certain distance, probably not. Thought it isn’t common to use so big textures in games.
Perhaps it would be better to ‘split’ the texture into small tileable patches (grass, dirty, mud, rock,etc), and use a lower res texture as a mask for mixing them.