1) The st170 has its own unique ecu (oak iirc??) which apparently wasn't a ford ecu so I believe is not a direct swap and would require changing the loom

2) Where are you taking the coolant temp reading from?
The focus rs engine will read over 100c (on a scangauge reading from the obd port) I believe this is a head temp and not the actual coolant temp, the fans should kick in around 106c. Otherwise check your plumbing, your rad and your fueling.
I'd go for any aftermarket rad designed to be used on the focus rs

Hope that's been of some use