The easiest thing to do is use your tax planning software (or a blank 1040 form and pencil) and plug in what you think your new numbers will be. You'll see how much extra in taxes you'll owe and can plan from there.
It will be easier to have your and your spouse's employers withhold more income to compensate for the freelance income, rather than making estimated payments... but that's optional of course.
It sounds like for your situation, I would just stick with the Roth IRA for the time being.
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