The front will normally have a higher ride height than the rear. However, lowering springs will lower the fronts almost twice as much as the rear, so it doesn't hurt to go with new springs front and rear. You may want to also add new struts, via a package like the Sachs kit, or an HR/Bilstein package. Both will run you around 600$.
Also, I think that larger wheels tend to exaggerate the gap between the top of the wheel and the fender, or at least make it more noticeable.