Use both! EBay is a ready-made pool of potential customers who come to the site with their wallets open. So, if you're just starting out, I would learn the ropes on eBay first. But you can drive traffic back to your own website via eBay. Once you are established, it makes sense to build up both sites. Eventually, each will draw visitors from different places, which can only help your business as you diversify your customer base.
The fall in new company starts does not necessarily mean that the American economy is less dynamic than it used to be, or that Americans are opening up new establishments at a lower rate than they did in the late 1970s.