The first post in this thread has all the size information you need:
https://www.fiestastforum.com/threa...ze-bolt-pattern-offset-tire-information.1126/
The OEM wheel is 17"x7" with a 47.5 mm offset. The bolt pattern is 4x108. The hub centric diameter is 63.4 mm.
The wheel you want will be 16"x7" with a 42-45 mm offset, and the 4x108 bolt pattern. If it is made specifically for the Fiesta it will have a 63.4 mm bore. If not, you'll have to use hub centric rings to mate the bores.
The closest to OEM diameter tire will be 205/45R16. (0.2" shorter diameter)
You can use a 205/60R16 as well (0.5" taller diameter)
Either of those will retain the stock section width, avoiding problems with clearance.
Most wheel/tire vendors will have an online selector that has you put in the make and model of car, then allow you to select the desired wheel diameter and will then show you what is available.