You are right in that you would have to base the estimated taxes on the prior year income tax liability. Since you do not have any idea how much profit is going to be generated in the new small business, the only question I have is did you work during the year and was there sufficient federal income tax withheld on those wages earned during that time!
Clearly, if you think the business is going to be profitable and your AGI is going to be greater than the prior year then you would want to make an estimated tax payment in the 4th quarter. Please refer to the following link for additional guidance on this.
Can you please explain when a taxpayer is required to pay estimated taxes?
