1. Based on the above information, do I miss anything?
No. You stated how the process for filing your taxes correctly.
2. Do I have to file the e-commerce business tax quarterly? What's the benefit of filing it quarterly?
Yes. If your payments are not timely, the IRS will assess late payment penalties.
https://www.irs.gov/businesses/small-businesses-self-employed/self-employed-individuals-tax-center
2. Am I considered the self-employment? Should I file the Schedule SE?
Yes. Even though you have W-2 employment, you also have taxable self employed business activity.
Yes. See above link to the IRS website.
3. What is a Quarterly sales tax and Quarterly Self-employment taxes? Do I need it?
Quarterly sales tax are remitted to your local taxing authority if you are selling items or products where sale taxes are required and charged.
Quarterly Self-employment tax is a tax consisting of Social Security and Medicare taxes primarily for individuals who work for themselves. It is similar to the Social Security and Medicare taxes withheld from the pay of most wage earners.
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