Self Employed Federal Tax

Hi,

 

I am a full time worker (on company W2) and my wife is  self-employed. I have some questions around tax return filing and optimizing tax benefits:

 

1. Is it more beneficial if we file our taxes separately or file jointly? For around $12,000 self employed income?

2. Quarterly Tax prepayments: In 2021, we have not done quarterly tax prepays, as we did not know about it. How much penalty are applicable, if the income is about 12,000 for the year.

3. What all taxes are applicable on Self-employed income? For example, do we pay for both the employer and employee Social Security Tax and Medicare? Is 15% tax bracket is a good guess for federal tax? Any other taxes that are applicable for self employed personal?

4. What other qualifying expanses that we can deduct so as to reduce taxable income? The idea of filing separately was to use standard deduction on income to reduce income tax. Is it a valid assumption?