thanks guys, really appreciate all the tips and experiences you have. yes at this point GPU is not an option since the project is now ongoing and in full swing.
yeah in the end refractions are just a bitch to render xD i hope they can do something about that in the next release. one of my main problems with corona compared to vray is, that i dont know how to tackle noise properly. they tell us to leave the performance tab at default but when renders look like that, basically unusable you have to tweak something. and thats where my problems start. there is no in depth video explaining the ins and outs of what to do when X happens.