Hi. Check out procedural mesh component, You’ll probably need to make chunk based terrain. For mountains i would recomend simplex plugin https://forums.unrealengine.com/showthread.php?94847-Plugin-Simplex-Noise-1D-2D-3D-4D-Fast-Perlin-Noise-Version
My first infinite world was based on hierarchical instanced static mesh component(it’s easier, but it’s minecraft like terrain), but procedural mesh component would work much better.
Good luck.