Ford of Europe has used 4 x 108 for a very long time, never 4 x 100. I don't get the issue people are having with 4 x 108 wheels, there are a ton of great wheels available in 4 x 108. The Focus/Contour guys have been using 4 x 108 wheels and there are many awesome looking wheel packages installed on their cars. You could do what I have done if you find a wheel you have to own, but it is 4 x 100, which is just have them machined for 4 x 108. I did that with my Axis Touring cups back in 1999 and have been using them ever since.
Since there isn't a Mazda2 ST, you will need to drill all of your brakes to 4 x 100, and I would get a spare set machined since you now have a wear item that can't be purchased off the shelf.
If you want to go through all the work of replacing hubs, I would upgrade to the Fiesta R2 Tarmac hubs, rotors, and calipers. You get more wheel clamp load from 5 lugs, better load distrubution, and rally proven hardware. I am pretty sure the R2 Tarmac uses AP Racing calipers. I have only seen the R2 Gravel kit since there aren't too many tarmac events in the US. The R2 gravel brakes are pretty impressive, but the tarmac ones are even bigger.