@SJHoodlet You can buy a bundle and save, but make sure you plan to use them. They are not transferrable.
I went through IngramSpark, and their cover template generator made me a bar code so I didn't have to pay bowker anything more.
You WILL need a separate number for each format.
If you have a login for bowker, you can get a listing of all your isbns that you own. You can also enter info about your book there. They claim it makes your book more visible to buyers, but I haven't noticed.