The best springs to get for the Focus are the Eibach's. They lower the car 30mm and can be purchased from Ford, as they were an option from new. They come very highly rated from all Focus owners on FFOC. I had them on both of my Mk1 Focus's.

I ran 17" on both. Had 205/40 & 215/45. The 205's I found to be very hard and not as comfortable as the 215. They were also like rubber bands, very thin looking.

Andy