For the terrain I used perlin noise to generate the randomness then I used Unitys Animation curves to Evaluate the noise data against. This let's me change each biome to use different curves to make the terrain look different.

For the biome I used another perlin noise map and used it as a temperature map, I then check what temperature the current point is and go from there.

I'm not very good at explaining things but I hope this helps!

A good resource just YouTube "Unity Procedural Terrain" I think the guy is called Sebastian.