Well see the whole thing is there is not much capital involved. The business will be purely digital meaining the storefront will be a webpage. No overhead other then maintaining the site and paying a few employees to gather/ship the goods. Only true risk is getting it off the ground and possibly losing the initial capital.
As for what Id be supplying it would be as Craig said niche items meaning interior parts exterior accessories and perhaps a few engine components. The parts themselves can all be obtained NEW with the price reflecting that but used parts can also be had and that will depend purely on supply.
Right now Im just weighing demand. Like I said I know the Honda JDM market is alive and kicking but I hear very little from the other makes. Perhaps Im just not paying attention?