Scale and architecture first, then carving, and only then sheets from the same geometry.
Take scale from the drawing or from a photo by calibrating perspective
Build the architecture as exact BRep: casing, frieze, corbels, a cornice at 22.5°
Model the carving as separate meshes: rinceau, acanthus, rosettes, egg-and-dart, trimmed at the ends
Break the piece into parts for milling from foam or HDU
Generate sheets from the same geometry: dimensions, sections, installation