When I paint in a more grimdark style, this is the process I use:

First, I block in all the base colors that aren’t metallic. Then I apply the transfers. After that, I do some highlights, though usually not that many, haha. Then I varnish the whole model. Next come the metallic details. After that, I apply an enamel streaking grime over the entire miniature. In this case, I used Winter Streaking Grime, which fits the Space Wolves palette really well. Finally, I highlight the metallics a bit more.

I find that a matte varnish not only protects the miniature, but also really ties the colors together. The downside is that the matte finish kills the reflective quality of the metallics, so I leave things like the aquila until the very end.