Hi Jeff,
#2 & #3 are natural "makes sense" progressions.
I'm not sure how a gateway page would reduce click throughs. It does not have to be the index or start page for a domain. It simply needs to be the page that indexes with SE's. One page is by no means a miracle. The BEST method to get SE ranking is still static pages (or appear static to SE's in all output even if dynamically generated) with specific content directed towards SEO.
Search Engines (specifically the big three) can generate more click through than eBay does for a particular vendors listings. Its the difference between heaps of vendors within eBay selling same items .vs. a highly directed content at SE's where click through leads to the Auctiva store.
Of course, when the prospect customer reaches it and see's eBay then the decision to purchase, not etc. all comes back into play. While eBay is still considered the #1 marketplace I know for certain that many a retailer have had significant traffic increases and conversion due to people tired of the "ebay experience".
Tis' also why I said how much money do you all want make?