I mean this is the nicest way possible, but you really shouldnt waste your time and resources on this. The retail sector is brutal at best and these are testing times for any business.
Your bringing to market, something that is already available, all be it overseas. By the time you sort the supply then you'll need to worry about HRM customs an excise, you will hemerage profit from every pore when you get to this point.
The biggest problem i can see, is the fact the product is just for the mk5 golf, who's going to buy one? Most enthusiasts and tuners/barrys have limited funds at the moment as a lot of people are being put out of jobs. The lust for buying parts will still be there but the funds wont.
As a group buy or something in small numbers yes, but you wont make any profit on them.
As i say im not trying to be an arse i'm just trying to help