How to create a terrain material, with 10+ procedural texture layers with alpha?

hello everybody, This is my first question from unity (and just started also working with Unity) :)

I need to convert my E-On Vue project to Unity in the most simple way possible. Vue is a high poly nature modeling program (sample incl). The terrain is based on a brushed heightmap in photoshop. Every single vegetation (like gras, forest, earth, roads) is created by a seperate procedural texture in Vue, with a seperate black and white texture that is used as alpha for every vegetation (alpha is projected like a heightmap on the terrain, so it has the same size, not tileable). After that i need to drive both my ground materials and vegetations by procedural density materials and alpha textures.

I've started in unity to create a terrain, and loaded the RAW heightmap (4096x4096). That works (alhough the height is not correct and have to guess). I then imported the obj of the objects, all works well. But now the difficult part, the terrain textures and vegetations.

Are there any solutions or suggestions to create this? Unity has procedural textures, but i've read that mulitple textures with alpha channels are a problem. The alpha channels should be 4096x4096 px. I have round 10 vegetation layers.

I've uploaded an image with the Vue terrain and the textures with alpha projected on it (added random colors to make it clearer). Second on top is the result in Vue

Thanks!