Will the IRS go after my CPA for messing up my taxes? How?

Yes, you can. But it is not easy to do. You have to prove the CPA made a professional mistake that he or she should not and that the mistake caused you financial damages. Your damages from his malpractice is measured as the additional amount you have to pay the IRS over what you should have paid. If the CPA assisted you in filing a return that showed you should pay less than you should have, the CPA did not cost you anything. The CPA saved you money. In most cases, the damage is only the interest and penalties added to the amount of tax you owed. You already owed the tax to the IRS so the CPA would only owe you the penalty and interest for late filing and late payment. A smart CPA will often offer to pay this for you. I suggest you try to work with the CPA to fix the problems. Often a good CPA can save you as much off your taxes as you will owe for the penalties and interest.

Perhaps. The issue will be whether the CPA failed to exercise the professional standard of care that a CPA in your area would normally exercise. Keep in mind, if the CPA did breach this standard of care, the CPA will not be liable for reimbursing you for the taxes you paid (you would have paid those if the taxes were properly prepared), but only for the interest and penalties you pay.