Your best bet for Maryland laws is to contact your local State of Maryland tax office. Any advice you get here and on most other forums is likely to be WRONG.
No idea on Maryland laws, but I suspect that they mirror the Federal tax approach. A sole proprietorship means to the IRS that you, personally, are in business. All income that you generate from all activities (employment, business income, product sales, consulting, etc.) are reported on your personal tax forms. You may also list business expenses as deductions. But you need to know which ones are eligible and how to do this. You need a tax accountant to tell you what to do and how to set up your records, etc. Just because it is a sole proprietorship does not mean that it is simple to account for business revenues, expenses, and income. You need expert advice on this.