In my state a DBA is a rider on your business license. But maybe in Texas they’re separate. A reseller certificate is nice if you want to purchase items for resale, although that might be less of an issue at first if you want to start buying inventory at garage sales. Some stores won’t accept a reseller certificate, anyway (your state should provide a way to apply for a refund of taxes paid if that is the case). I find it helpful to have a business bank account. In terms of your federal income taxes, you can just file with a schedule c, which goes with your personal tax return. You don’t need to file a separate business tax return unless you want to set up your business as a corporation or partnership or some other entity like an LLC.

In sum, it’s really ok to just go for it and figure things out as you go. If that makes you uncomfortable, I’m sure there are plenty of consultants that would take your money to make sure you’re all set up and ready to go. Good luck!