We can only give tax advise and I would recommend that you should first consider incorporating as either an LLC or a corporation. An incorporated entity will offer you protection and will allow you to project a better image. You need to get a new EIN# as well for your business, maybe your CPA can help with this as well.
I am afraid I cannot provide any advice regarding the online selling business or how to get started with your business. But, I can suggest that you contact your local state tax authorities as they may have tips for new business startups.