To set up withholding for Social Security you will need (you and your spouse) to file form W-4V - Voluntary Withholding Request. Here is a link to that form:
https://www.irs.gov/pub/irs-pdf/fw4v.pdf (you may need to copy and past it into a browser to bring up the form)
The amount you can have withheld is limited (see the form for details). You could have the remaining amount deposited into a separate account for you to make your tax payments.
Spousal benefits are a bit complicated in that your spouse must be drawing a benefit for you to qualify. Social Security will also look to see what benefit you qualify for and pay the greater of the two amounts (even if you do not want to draw "your" Social Security until 70).
Any benefits you receive will be reported and taxed the year you receive them, so you will not need to amend your 2020 taxes.
I do want to suggest that you consider talking to a financial planner regarding converting your Traditional IRA's to Roth IRA's. The conversion is taxable and is considered income, so you may have a very large tax bill. The increase in income in the year of conversion may increase the amount of your Social Security is subject to income tax and your overall tax rate as well.
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