Wow. What you have there is really impressive so far. It's definitely got an Old Masters feel.
As for advice, you probably don't need any! But just in case, the only thing I'd say is build up in layers, and use layer modes to simulate glazing (Color, Overlay, Soft Light), scumbling (Multiply, Darken, Overlay), and impasto (Normal mode).
I'm excited to see how you get along on this.
Nick AvalloneAngryFungus Art Blog