There are drawbacks to any rim change, at least aftermarket ones...
The Ford bolt pattern for the Fiesta is 4 X 108mm or 4 X 4.25 inch
Not too many Rims are there for Ford in a good price range for the common buyer.
The basic rim 14" ones anyways, are 4 X 108 and are 5.5J rim width and usually have a 43 ~ 47mm Positive offset Positive meaning it ducks under the brake caliper and spindle - so it's right under the strut and pretty much centered at the pivot point. (Ball Joint and Strut pivot inclusive)
Then the Rim width goes up from that to 6 inch wide 4 X 108mm 6J type being a 15" rim default
There is 16" with 6.5" width and are 4 X 108mm with a 35mm Positive offset.
So in reality the 4X108 is what you're stuck with.