How do I sue and which court do I seek for a lawsuit regarding a default in payments?

Generally speaking, you are in a very good position with the promissory note.  I would take it to an attorney to review to give you an idea as to how you need to bring the suit.  The note itself may speak to the issue.  There also may be certain requirements on your part like sending a notice of default or a demand for payment. Make sure that you do indeed comply with the requirements because it may be necessary for you to act before you can sue.  It is known as a condition precedent.  You may also need to give them an opportunity to cure the default (calls and text are generally not the preferred or legal method).  Good luck to you.

For several thousand dollars definitely speak with an attorney and let the attorney help you. If you want, you may be able to ge,t the attorney to take it on contingency, which will reduce your potential recovery but also reduce your expenses and risk. Note that if the owners have no assets or have declared bankruptcy, you won't be able to collect even if you win, so if you have or can get any sense of their financial status, consider that point and also share the information with your attorney. Also decide if you are willing to settle for less than full and, if so, how much less. Possibly see if your attorney will agree to a price or cost scale where he or she gets less if the case settles quickly before trial.