Estimated Payments

Individuals can base their payments on:
90% of the current years tax or
100% of the prior years tax or
110% of the prior years tax if the prior year's AGI is more than $150,000 ($75,000 if filing Married filing Separately)
Note that there is no penalty for not paying federal estimates if the current year's tax is less than $1,000 or there was no tax liability in the precedding year.

No. Estimated tax payments should not be combined and sent with or be included in checks or money orders for payment of federal income tax with your 1040 tax return. Mail your estimated tax payments separately to the address shown in the 1040-ES instructions.

Generally, you must pay estimated tax for the current year if you expect to owe at least $1,000 in tax for the current year, after subtracting your withholding and refundable credits and you expect your withholding and refundable credits to be less than the smaller of: 90% of the tax to be shown on your current year tax return, or 100% of the tax shown on your prior year tax return. Your prior year tax return must cover all 12 months. These percentages may be different if you are a farmer, fisherman, or higher income taxpayer. You do not have to pay estimated tax for the current year if you were a U.S. citizen or resident alien for all of the prior year and you had no tax liability for the full 12-month prior year tax year. You had no tax liability for the prior year if your total tax was zero or you did not have to file an income tax return.

Yes. If two-thirds of your gross income is generated from farming, a estimated general rule exception exists. If you file your return and pay the entire tax due on or before March 1st, then you are not required to pre-pay amounts with estimates.

You may fill out IRS Form W-4V, voluntary withholding request. Speak to your local CPA about getting a copy of this form.

In a calender year, non-farmer taxpayers must make four installment due on April 15, June 15, September 15 and the following January 15. If the 15th falls on a weekend or holiday, it is due on the next work day. For fiscal year entities, the first installment is due on or before the 15th day of the fourth month of the fiscal year. The 2nd and 3rd installments are due on or before the 15th day of the sixth and ninth month of the fiscal year. The final installment is due by the 15th day of the first month of your next fiscal year. Farmers and Fishermen only make one installment payment by January 15 of the following year.

No. The filing of joint or separate estimated payments does not require that you are committed to filing that way.
However, you will need to advise the IRS as to how to allocate the estimate payment.
Often this can be an area of difficulty when individuals are going through a divorce and have decided to file separately after making joint estimated tax payments.