i've had a couple mate, fiestas and escorts. they are awesome!!
they rot everywhere though, u need to check the sills, under the windscreen, arches, battery tray, filler cap, behind the doors, boot lid, floor pans, around the sunroof, the lot.
the good thing is, you can still get all replacement parts for them. check the bottom arms, all the bushes, brake pipes and shock absorbers.
make sure tyre wear is even, and the car drives straight.
the engines are pretty much bullet proof, check for blue smoke on start up and white smoke when the revs are high, the cvh engines always sound tappety. also make sure the turbo spools up properly, they are expensive and u don't get loads of white smoke when it is spooling.
make sure the car has had no accident, history is vital, make sure its not a stolen recovered either, there are loads of them about. mileage wont be an issue as long as its regularly serviced and maintained