Thanks for your reply, sorry for letting you wait. I wanted to try the newest software versions and UE made me install all the newest Visual Studio runtimes but didn't tell me to do so :D Took me a while.
So what can I say. I still get the same error message (see screenshot) but the imported model looks ok. Of course this had to happen :P A few months ago I was trying the same thing and there was phong-shading errors / facetting everywhere. But I still wouldn't feel comfortable working on a project in UE when there are those missing smoothing groups errors all the time. Or can I just ignore those and it's still ok?
I know how to use the UV System in C4D, I bought 3DKiwis bodypaint series when it came out and also used this a lot during my work for some characters. The last time I tried I couldn't test the UV parts because the shading was weird.
Well I guess I'll have to give it another try now :D