| Well, it seems that you receive a big refund, although I am not sure of the amount, but, clearly if the refund is greater than the additional taxes you will incur because of your self-employed income, you can avoid paying the estimated taxes.
Further, if you don't mind owing a bit of taxes at the end of the tax year, then the anticipated refund will reduce the impact of the additional tax liability. Once again, you can avoid paying the estimated taxes.
If your self-employed income increases substantially, then I really suggest that you should start making estimated tax payments to avoid potential large tax liability at tax filing.
But, pay careful attention to avoid penalties and interest on underpayment of taxes. Make sure your spouse increases his withholding accordingly as explained earlier in my previous message. | 
