Our Limited came with 18" rims would 17" fit?
Yes. FCA equips the Pacifica with either 17", 18" or 20" wheels depending on model or options. Use the same tire size as FCA uses and there should be no problem. You do need to make sure the wheel (rim) itself has the correct bolt pattern, back spacing and brake clearance as original as those are variations within wheel sizes.
2017 Pacifica Limited (built May 2016)
Vacuum delete, KeySense and Tow