This is just my two cents for you..
Don't design, buy tried and tested. Check out Don/Smittys link above. There's a book i recommend you buy or source.. its called "Poorly made in china" and it will open your eyes to dealing with the far east.
I fly to Hong kong twice a year and design CCTV cameras, and i take two very good translators with me where they proof hear each other to ensure that the smallest detail is not mis understood. the factories will even make YOU design the quality control procedures and if you are not very well versed in QA and QC theres a good probability something will be wrong when you receive your stock. I tend to find it takes three attempts before they put something infront of me which is what i originally wanted, and if you overlook an issue and sign off on the order there is no turning back and its your loss to write off. The last time i was there i had an hour long argument with a CCTV factory, about what IP66 and IP67 means.. my god.... I am a patient man... but this tested me to wits end.
As far as they are concerned, they put IP66 on the boxes of cameras which are indoors only.. and IP67 on boxes of cameras which can go outdoors.
I had to not only educate the factory that the IP numbers actually do mean something and you couldnt just pick a number and put it on the packaging, I had to design a quality control line for their factory so they could submerge the camera's for 12 hours, expose them to jets of water for set time periods, soak test them with voltage, and so on and so forth..
My point is, just because you find a factory which specialise in a product - do not assume that they know what they are doing in any shape or form.
And by the way, when you get all that right and are happ with your product, you will have to go through it all again on your next order you place, as you cannot just say "The same as last time" ... you have to check the samples to make sure it passes your QC.
And lastly.. watch out for your shipping. nearly always what they quote is to transport your items to the docks, not to deliver them to you.
Good luck with your venture