Hey,
Nice to know about your business plan. You have the right decision of first building your inventory. I have a simple suggestion for you in this regard. If you will be using certain standard parts such as screws , electrical pinouts etc, first try ask your supplier to provide the CAD model for those items. I am sure that can reduce some of your work.
Now let me explain something about myself. My name is Gaurav Jalan. I was working as senior project engineer recently with North American lighting Inc, USA. I was designing automobiles headlights and taillights for different OEMs mostly Honda and Toyota. I am completely aware of the kind of work you need to build A surface for such parts. I have now recently started my own company of product design and development and I will be more than happy to help you in your design work. You can check my profile at linkedin as well. I can do all your thickness checks, draft checks, surface curvature checks, sink check, clearance check, Parting line check, and i will also try to get mold flow check for you as well. May be you may not need all these checks since you are trying to use an already developed part. But in case you need it should be no issue. I am working with CATIA v5 software and other add on such as geo caliper for thickness, moldex3D for moldflow etc.
let me know what you think. Budget wise I am sure its going to be costly. Not that easy of a task. Good luck in your endeavor. You are welcome for more questions on design