What you really need is a good business attorney or a CPA to assist you in setting up your business properly, not the least because there are too many facts and issues that need to be taken into account than can be described in one question post on Avvo. You also need to speak with someone familiar with setting up a business in your local area because there are many issues that are germane only to your locality - such as taxes and licenses needed for the town or city you live in - that can only be adequately handled by an attorney or a CPA in your area.
Unless things have changed, Congress imposed a moratorium on the collection of sales tax on sales made through the Internet.
Some states, as in NJ, allow a reseller, to avoid paying sales tax on purchases, but need to collect on sales to NJ residents. This is why my colleague suggested you speak tto a CPA.
Yes, it is not a bad idea to establish a corporation or LLC through which to conduct this business, and to maintain a separate checking account for this entity. Depending on what type of entity you chose, you will be required to file a Certificate of Incorporation for a corporation or a Certificate of Formation or Organization for an LLC, and then register the entity with your state's Division of Taxation. Taking a wage from a corporation will require the withholding and payment of payroll taxes, while taking a draw from an LLC will require that you pay estimated income tax.
By all means speak to a local CPA and/or business law attorney.
The foregoing is not intended to be legal advice upon which you may rely as I have not been retained for this purpose.