If you can max out your 401k or max out your IRA and then save an additional 20%+ of your after-tax, after-retirement contribution, good things really start to happen. If one is looking for earlier financial independence, such as retiring in their 40s or early 50s, it may be a good idea to skew towards more after-tax savings and investments given one has to wait until 59.5 to withdraw from their 401k or IRA penalty-free.
According to Uncle Sam, you need to be "materially involved" in an enterprise to earn active income. With passive income, it's just the opposite, as the IRS deems you to be earning passive income if you're not materially involved with a profit-making enterprise. By and large, expect income to be taxable if you are engaged in a passive income enterprise. You will need to report earnings to the IRS.
I have only dabbled in drop-shipping before when I had an eCommerce platform 6 years ago or so. I think it is something that you could do on the side, but you would want to do in depth research on the industry you want to get into before setting up shop. It may be a little less passive up front, but over time you could take your hands off the wheel.