in MapBuilder2, free/extra users can use the terraintex fixed function effect, which uses blending based on tile maps alpha channel, while commercial and pro users can use a shader with nearly similar blending rules (a bit better).

I modified the terraintex ffe to work with mirror views like water by putting a 24b texture to the 1st skin (that appears in the mirror view). the shader also has a 24b base texture on the 1st skin, but it is also used to blend in a bit to hide the repetitiveness of tiled textures.

in theory in a shader you can define texture sizes and tiling independently... but easier to use similar ones. you can take my textures for free from my editor package. they are 512x512. but there are many free sources, or you can make them from photos too.

moreover, try to use L3DT or a similar terrain generator to create more realistic terrains than handmade ones, what you can modify afterwards to the needs of your game. I used it for the example terrains, and I simply smoothed out in my editor the middle regions of the terrain where I wanted to put some buildings for my RTS game test level.