Hi postman,
You seem like you've been doing really great! Thumbs up for you!!!
One of the benefits that you will notice right away is the lowered listing fee. With your selling profile, you are ready to open a store. If it's necessary? I'm not sure in your case you're already doing so well even without a store :)
But any how to give you a more detailed list of reasons as to why you should open a store on eBay, please go through the following blog posts and guides -
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Hope this helps :)