I would create a mask from ao, curvature and a grunge map an use that as a starting point for roughness. Fiddle with that until you get something with more variation I would also add some blurred noise as a normal - masked by ao - in order to create some dents and wobbling in the surface
From my point of view, firstly decide whether this piece is purely decorative or votive. In other words the former could belong anywhere indoors or out but typically if the latter, then most often an object of devotion will reside in a purpose built covered shrine which generally determines what level of patina, to apply.…