You'll also need ecommerce software, fulfillment software, worry about warehousing, customer service, refunds and so on. But that's not all. You'll also need traffic. Think search engine optimization, Facebook ads, and other social media campaigns. Sound like a lot of work? Sure, it is. Especially if you do it all on your own. You could opt for Amazon's platform, which might be the easier route. But, then again, at the end of the day, this is a serious business, which could produce significant profits. So you're either all in or you're not.
Considering that you have a finite amount of time, passive income should make up a large part of your work. And if you're serious about generating any semblance of income online, then passive income should be one of your sole goals and ambitions. Why? Simply this. Wouldn't you prefer to do the work one time and get paid repeatedly as opposed to relying on your time to generate that income?