Looking for the best way to make a terrain for FPS. I need to have the terrain textures high enough quality that looking at the ground at camera isn’t pixellated, but also able to look into the distance with seeing tiling.

Is the secret just really really good textures? Or is there a trick to building the terrain and using splatmaps?

" is there a trick to building the terrain"? Yes. In painting it (which is really just changing the SplatMap.)

Use two similar textures (or even the same texture twice) with different sizes. Use numbers that rarely line up. For example, for size 15, the other should not be 5, 7.5 or 10. Maybe 11.6. Unity allows you to adjust sizes and see the change right away.

Then use the second “pretty much the same” texture to brush over the first, with “random” strengths. Each texture will hide tiling of the other. For very far stuff, can use the same trick with a very large size (not the texture size – the size in the Terrain painter) and brush it on very lightly.

You can get away with surprisingly small, high-contrast textures, with tricks like this.