Gate 4: Manufacture
What's the hardest part of all this? The answer to that will vary from person to person, company to company, and project to project. But without question, the gate with the greatest number of steps, the one with the most unknowns to a newbie, is Manufacture. Now you put your design in the hands of others who have the facilities and knowledge to produce. Getting that done well, it requires skill, experience, and careful communication. A seasoned engineer once told me to consider the path to manufacturing the same as to having a child: Nine months.
After our startup was bought we had to learn very fast about scale manufacturing, USA vs. China, early stage vs. mature. It was hard, and full of friction. You will be creating tools, creating your sub-assemblies, testing tools, doing first runs, and making trips to China or Wisconsin. Distance presents a challenge, and I highly recommend that you start in the USA (or your home country) and only later consider scaling elsewhere. Once again, this is the time to get cozy with companies like Dragon Innovation and PCH as you start to understand tooling, certifications, regulations, logistics, and customs.
Fortunately, some of my friends at Microsoft's XBOX and Amazon's Kindle helped me think through this process, filled with questions and check-offs for you and your manufacturing partners before you kick things off. I'm also grateful for the good folks at Synapse that always help our small Seattle community with a plethora of information about this subject. If you make it through the following list, you are closer (though you never feel totally ready) to passing this gate.