There is no single checklist for every project
A simple solitaire, an organic pendant and a ring with a halo and pavé don’t need exactly the same information. A long, fixed list can ask for unnecessary details while missing the question that really matters.
For a ring, the size is fundamental
Finger size affects the entire structure. Even when working from a photo, you need a value that ties the image to a physical scale.
For a center stone - dimensions before carats
For CAD, the physical dimensions of the stone matter more than its carat weight. Two stones of the same weight can have different geometry.
If there is a target weight, define what it means
Clarify whether it is the weight at casting or of the finished piece after cleaning, polishing and setting. A short clarification at the start can prevent a large gap later.
What in the photo must stay, and what is only inspiration?
A reference can be an exact instruction or a design direction. It helps to know whether there is professional freedom to suggest improvements in proportion, design or fit for production.
You don’t need to know CAD to order CAD
A client can send a photo and say “I want something like this”. An experienced modeler’s job is to read the piece, identify what is already clear and ask only for the information that is truly missing.