Even if your income is less than the Standard Deduction and you don't owe any regular income tax on it you will owe Self Employment tax. For SE self employment tax - if you have a net profit (after expenses) of $400 or more you will pay 15.3% SE Tax on 92.35% of your net profit in addition to your regular income tax on it. So if you have other income like W2 income your extra business income might put you into a higher tax bracket. The 15.3% self employed SE Tax is to pay both the employer part and employee part of Social Security and Medicare. So you get social security credit for it when you retire.
Don't understand your second question? Are you asking about business expenses on your 1099 self employment income? You only send in the estimated payments. You enter your 1099 income and expenses on schedule C in your personal tax return due in April. It's all combined on y our tax return.
Don't confuse itemized deductions on schedule A with your business expenses/deductions on schedule C. They are separate. For Schedule A personal deductions, you get to take your itemized deductions or the standard deduction, whichever is larger. Itemized deductions are things like Medical, Gifts to Charity, State Income Taxes Paid, Mortgage Interest, Property Taxes, Car Registration fees, etc.
You get to take both, your business expenses AND the Standard Deduction (or your personal Itemized Deductions).
