You could buy some Daemon Prince bits from somewhere and use the armor plates there.
Greenstuffing looks difficult but its not that bad. The biggest issue is leaving your finger prints in the item you sculpted.
I saw an armor tutorial a little while back for Khorne specifically that showed how to make the armor look like it had been made out of hammered bronze. You make the basic shape as normal, flat as you can make it. Then you take the rounded end of a paintbrush and make little divots all over. To look like it has been hammered out of a sheet.
Bitz barn has just about every warhammer and
40k bit out there.
http://bitzbarn.com/