Stores save you money, Auctiva saves you money, and a domain name will direct buyers to your eBay store.
Unless you have a stand alone expensive website with many items for sale and is linked on other sites, no one will ever find your store. Who gets top listings on Goggle? Just the megastores.
None of us love eBay but they have millions of ads on search engines and links on websites directing buyers back to your store. I was listing on ebidz (one of eBays small competitors) as a trial and at the top of their page there were eBay adds, that's just wrong!! I have seen links for my fishermen sunglasses on fishing websites and have gotten sales from them.
Log on to eBay and read the store tutorials and and fees, and then make your choice. Also read the advantages of listing with Auctiva (cool templates etc.). If you are just selling yardsale items you don't need a store, but if you are buying wholesale and have many of the same items for sale a store work fine. I hope this helps, you need to do your homework and sleep on it for awhile, and good luck.