From the looks of it, you are ready for an eBay store :)
eBay's official recommendation on this is that sellers should not even think about opening a store until they have at least 25 or more listings on eBay at all times, and you mention that you have finally gone over your 30 free listing/month!
But it is often recommended that for new sellers, they should wait until they have been selling for at least 3-6 months on eBay as well, and until they are already generating at least $500 a month in sales. - I guess you are beyond being a new seller!
You may refer to this guide for a list of benefits - Link hidden: Login to view
Also, i am a bit confused. With a store, if I list an item and say here are 100 available, do i only pay the listing fee for 1 item, or 100? if it is for just 1, then I suppose I see where the saving is.
You can sell multiple identical items if you create a multiple quantity fixed-price listing (Buy It Now or Best Offer) or list each item separately. eBay views this as avoidance of charges because the seller pays just one insertion and one final value fee instead of paying fees for each item.
You might find these helpful - Link hidden: Login to view
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All the best and good luck with your upcoming eBay store :)