I've seen that Marvelous Designer has the most realistic looking garments with lots of tiny wrinkles etc.

I'm wondering what would be the easiest workflow to get content from MD to CC (and then later to a real-time model suitable for UE4). I've seen that MD models have really high poly meshes and usually people do manual retopology and then bake the details as normal maps. Are there any "shortcuts" of CC3 specific tools that would help with this process? Avoiding manual retopo would be awesome but I'm not sure if CC can help with retopo using its LOD generation tools.

Honestly this is all you really need, I've adopted it to my work flow and it's amazing.

https://www.artstation.com/artwork/zZOOL

I use TopoGun for retopo, but something you COULD try would be to use Zbrush's ZRemesher and freeze borders/edges. Also you can adjust your topology in Marvelous Designer to some degree, and you can further LOD it in CC3 with InstaLOD. But I'm sorry to say nothing is going to do as good as manual retopo. I use this method for my UE4 characters.

Is it better topgun than maya for retopology. Because in your sample you have maya.
Please let me know. Thanks!!

With the new version of Marvelous Designer, you can avoid that retoping by being able to retop inside of MD9