Open an item then scroll down to the Description box and look up over to the right ... the Item number is in the upper righthand corner area. On your Active list there is a column that shows the Item number for each item.

You can search for Sellers via the Advanced link to the right of the eBay Search window. Scroll down to the Seller section and enter the ID and complete the Search at the top or bottom of the page.

If the listing is current and indexed, you can search by item number by entering the number directly into the search bar. Just paste your own item number of those digits at the end of the page address. That will work even if the listing has ended within ninety days or if it is not yet indexed.

I'm afraid records do not go back that far, there would never be enough room on eBay's servers to hold billions of items for a decade. Sold items can only be found in the past 90 days if you are on the Seller Hub, and for 60 days max. if you are on My eBay Selling.