personally i'd leave the extras in since the url to the item will be different.
expiration date - from the way i understand it, in the column that says expiration_date (in the file youre going to upload to googlebase) you want to put the ending date of the listing. it's supposed to be in YYYY-MM-DD format
Instructions related to the tab-deliminated file http://base.google.com/base/tab_instructions.html
I don't remember if it posted it, but here's a link to description of each of the columns in file, fomat of data that goes in there, etc. http://base.google.com/base/tab_attributes.html If you look at the file you created and look at this file, you'll see where some of the problems are (like the image url should be to a full sized image instead of thumbnail, the product type should be a more general label rather than ebay's category structure, etc)
And a reminder, cant put auction item in file unless it has a BIN price