The breach of the contract and its consequences will depend on how the promissory note was written.
It may, depending on the language, only be breach of the payment that was due but unpaid, but not a breach of the remaining payments.
Although you may have a great case to take to small claims court, just winning in court is usually the easy part. Collecting the money with a win from small claims is much much harder than winning, unless you have an extensive background in handling collection cases.
Hope this perspective helps!
If the payment schedule was written out in your promissory note and there was a date certain by which to make that first quarterly payment, then it might be construed that the entirety of the contract was breached and the entire amount is owing. However, as mentioned before, it depends on the true language of your promissory note as to what exactly constitutes a breach and if you can accelerate the total amount due and owing.
I also echo the sentiments on collection most likely being the hardest part. Just getting a judgment does not mean that you will receive money right away. A judgment simply means the debt is owed and you or your attorney have to find ways through the legal system to collect that debt.