Tax returns are only filed annually ... quarterly estimates are only needed if you will not have enough withholdings to cover your tax bill and you will owe $1000 or more.
Also you will need to report the interest earned each tax year so make sure you have an amortization schedule made up for both parties.
AND you may want to check and see if reporting the sale in full in the year of sale is better than the installment method for tax reporting ... it is an option even if you will get payments over more than one tax year. Going forward you would only report the interest earned and not the principal paid.
