why the hell do so many still use reverb? you will get the very noobish cavesound. for "expanding" the vocal tracks (rather dry) delay is the best thing.
As for growling, compression is a very neat tool. for example Åkerfeldt doesnt growl very load, but the compression levels it and gives a steady result. It also sounds like a slight amount of distortion was used, and that could be a neat trick, but keep the dist-level low, it shall not be noticeable in the mix really.
And about layering, it is sometimes cool, but sometimes worthless, like on Behemoths demi-god. The layering is parodic on that album, sounds way better the few times his growls are not layered.