Thanks a lot Rawalanche,
I’m actually installing Quixer Mixer, Bridge and Megascans and following some tutorials about how to mix them with Blender and UE4. I’m going step by step and I’m going in your way (use external tools). There is a lot of things which are unknown to me and which make me want to stop. I realized that the more I learn, the more I become aware of what I have to do. But it’s ok, I like it in a way 
I’m creative and resourceful, that should be fine, I hope
I understand things better day by day and I am determined to continue and start/finish it.