If the items are all exactly the same then the best option would be to use the Buy It Now listing format, setting the asking price at a level that would ensure that you got what you wanted for the item(s) sold once eBay and PayPal had both taken their cut of the final selling price. If you were to do that then so long as you listed the items using the Advanced Selling Template you would have the option to set the listing up in such a way that buyers could select the quantity that they wanted to buy.
If you are absolutely set on listing the items using the Auction template then you will have to set each listing up individually, but one of the disadvantages of doing that is that people are always going to look for the least expensive option, in which case if you list too many identical items all at the same time then your auctions may not end up getting a decent selling price at the end of the listing, as you may well just end up with the items that did sell only attracting one bid as a result of people always bidding on the least expensive one.
Should you decide to list the items using the Auction format then the best option would be to just list one item for sale and see how many bids you get for the item. If you get a lot of bids then in addition to selling the advertised item to the winning bidder you could also make a Second Chance offer to one or more of the bidders who lost the auction if the other available items are exactly the same as the one listed, with no differences whatsoever that could result in an Item Not As Described case being opened against you. If you were to do that then you may find that one or more of the losing bidders would accept the Second Chance Offer, in which case you could send them one of the other items, so long as each item is identical in every way to the one shown in the listing so as to minimise the risk of one or more buyers opening an Item Not As Described case against you.
