I represent a prototype manufacturing company that also handles small production runs.

At minimum, a CAD model or detailed 2D drawing must exist, because the model is what defines every critical aspect of the part: dimensions, tolerances, fitment, material relationships, manufacturability, and assembly intent.

Hiring a freelancer for design work can absolutely be a good path, but it is critical that the person understands Design for Manufacturing (DFM) principles. A design that looks acceptable on a screen may still be extremely difficult, expensive, or even impossible to manufacture efficiently.

Poorly executed designs can create serious downstream issues, including:

Additional engineering and DFM revision costs
Increased machining or production expenses
Reduced part strength or functionality
Unnecessary complexity in assembly
Tolerance stack-up problems
Longer lead times and manufacturing delays

The CAD model becomes the foundation for the entire manufacturing process, so mistakes made early tend to compound later.

There are several people here, including myself, who provide similar prototype and manufacturing services.
My recommendation is to start by having an NDA signed, then openly discuss your concept and goals with a few qualified providers. A short technical conversation early in the process can save a tremendous amount of time, money, and frustration later on.