1031 & contract sale

I own 20 acres of farmland that is divided into 8 lots. I rent it out as farmland as it keeps the RE taxes low and the market is soft. I have a developer interested in purchasing if I will finance it with a 20yr-5yr balloon. I plan on using the down to pay cost, pull 10K for personal and put the rest into a 1031 for purchase of a rental property. I understand the principle and interest tax differences on the mortgage payments. My question is at the end of the 5 years will I be able to put the final principle payment into a 1031 to purchase more income properties or will I have to declare it as capital gains and invest in after tax dollars?

You have to close on the new property within 180 days of the sale. You could park in TICs, but you may have problem getting your money out.