If I know my taxes will be much lower this year (retiring in April) compared to last year's, do I still have to pay the Estimated taxes? Say I have to pay $3000/quarter on Estimated because of last year's earnings, but this year it's even possible that I will receive a refund, so can I safely not pay those $12k? or do I have to pay them and then receive them as extra refund over several years? (and what about State's Estimated Taxes, same thing?)
There are a number or 'safe harbor' rules that apply to this scenario, but if you won't have any tax due at all, or are getting a refund, no need to pay more via quarterly.
90% of the tax for the year, or 100% of what your total tax bill was last year is the safe harbor.
Run the numbers you forecast for 2014, and see what TT tells you.