We try not to scale landscape much as it decouples your terrain resolution from it’s actual size. So say you were to sculpt the terrain now, your per poly resolution for terrain get’s less smooth. Which if the res was high before, didn’t really matter but if it wasn’t, it’ll be apparent that there are massive polygons for terrain. (not always a bad thing but you know, different games different needs).
The texture issue can be solved by shifting around the UV tiling on the material. If you’re following a tutorial it likely goes over that to get a proper terrain material resolution. It could also be the texture mipmaps. Are these megascans assets or custom?