3. Can I choose the standard deduction instead?
No if your spouse itemized on a separate return you also have to itemize. You cannot use standard deduction even if you have so few itemized deductions that they do not add up to your standard deduction amount. That is one of the many disadvantages of filing married filing separately. You cannot use the "same" deductions she used because the two of you cannot deduct more than 100% of anything. So you can divvy up the itemized deductions however you can agree to, but you both have to itemize.
Or you could both reconsider and amend the first return after it is processed and file a joint return.
If you were legally married at the end of 2020 your filing choices are married filing jointly or married filing separately.
Married Filing Jointly is usually better, even if one spouse had little or no income. When you file a joint return, you and your spouse will get the married filing jointly standard deduction of $24,800 (+$1300 for each spouse 65 or older) You are eligible for more credits including education credits, earned income credit, child and dependent care credit, and a larger income limit to receive the child tax credit.
If you choose to file married filing separately, both spouses have to file the same way—either you both itemize or you both use standard deduction. Your tax rate will be higher than on a joint return. Some of the special rules for filing separately include: you cannot get earned income credit, education credits, adoption credits, or deductions for student loan interest. A higher percent of your Social Security benefits may be taxable. Your limit for SALT (state and local taxes and sales tax) will be only $5000 per spouse. In many cases you will not be able to take the child and dependent care credit. The amount you can contribute to a retirement account will be affected. If you live in a community property state, you will be required to provide additional information regarding your spouse’s income. ( Community property states: AZ, CA, ID, LA, NV, NM, TX, WA, WI)
If you are using online TurboTax to prepare your returns, you will need to prepare two separate returns and pay twice.
If you file as married filing separately, and one spouse itemizes, both spouses must itemize. You can't use the standard deduction, even if your itemized deductions are zero and you pay higher taxes because of it. The two spouses can divide their itemized deductions any way they like; although 50/50 is the most common recommendation, the IRS will not object if you divide them a different way, provided they were paid from your common funds. (In a community property state, you must split income and deductions 50/50.)