A person putting 5 items up for sale more likely has a hobby than a business. The IRS has different rules for businesses vs hobbies (business deductions, home office deduction, etc). Why not try a few items as a hobby, and see what it's actually like first?
You might find the sales + fees + shipping come much closer to your costs than you expect. For example, on Ebay most items have a 10% commission, and most people accept PayPal (2.9% + $0.30). So if you sell a $10 item, you might owe $1 to eBay, $0.59 to PayPal, and another $2 or so to the post office for shipping. You might be out 1/3rd of your sale before even considering the price you paid for the item you're selling.
I think you should see if a few items sold on eBay works for you before worrying about if you have a business.