Just get started. I have been using this site with great success. https://www.freelancer.com/affiliates/bgriffey

I am working multiple ventures at the moment and the resources available on this site are tremendous. Very affordable high quality work. You can have an instant team of professionals.

I concur with the other poster. A 3D printed mockup is a great place to start.

I would not worry about your idea being stolen at this stage. Investors are going to be more concerned that the idea was someone else. For that sake seek patent pending when feasible.

The most critical thing is to get outing the market to validate the product. That is what business is really about.