jkemp: for the background I used just some sparkles footage, particular is a bit too tricky...
O/MI: thanks a lot! I recorded a timelapse while sculpting the helm: I duplicated the helm mesh, inflated it with a low negative value (like -2) and made it "emerge" where there were the gold parts.
jderiggi: thanks man! The video explains it all! I used the MAHcut mech brush to draw all the gold parts. It was lot of fun trying this technique, and really fast!
I should also credit Nick Zuccarello for the human basemesh under the armor: his free tool is really awesome!
I also took another render to show better the front of the helm, and a pair of full res details: I rendered it at 3k, and the render time was pretty good, about 70 minutes per render; this makes Zbrush a good choice even for print projects!