As Michael said, you could engage with designer or engineer to help ask and answer these questions. Ideally, I’d go to a vowin.cn' target='_blank'>product design firm like , or like many others.
Whoever you approach, I would advise you to observe how they approach your proposition. Anyone hoping to answer your question should probably ask a few questions of his or her own, first.
I could go on and on with necessary questions… you get the point.
I would avoid working with an individual designer or engineer. Almost all products are too complicated to do with a single person, and even two makes a world of difference. Some many times more, and you don’t want your eggs in one basket.
I would also avoid using a manufacturer for your design work. Manufacturers make their money from manufacturing. There are exceptions to the following rule, but generally they won’t be empathetic to your customer and they’ll try to design the product so they can make it (they’re very good at this, too). A good design appeals to your customer and is cost effective to manufacture, but perhaps through processes not at the factory you’re working with. If your idea is too early they may not even want to or be able to help you develop the product in the first place.
Lastly, I would recommend that you at least give prototyping a try before you hire a firm. You’ll learn a lot about your product, your customer, and your business. You’ll hopefully save some money. And you’ll be better prepared to engage a firm to finish it off for you.