liimey,
If you drop the car more than 1 inch you will have to install the bumpsteer kit and have a professional alignment done (caster, camber, toe, etc). A quality alignment job should be done anytime you lower the car at all (even .5 to 0.75 inches) to assure proper performance. More than an inch drop changes the tie-rod angle significantly and can cause the wheel to "toe-in" when you hit a bump. This toe-in causes the car to turn (when you dont want it to). Bumpsteer kits return the tie rods to the proper angle.
The Eibach and Steeda spring kits can be used with the stock shocks. Even better performance is acheived with their matched shocks/struts, but the stockers will work well.
Progressive springs *may* wear out the shocks faster than straight rate springs depending on the roads you drive. Most progressive springs are initially softer than stock (to provide suppleness), then get stiffer quickly to control travel/bottoming. Thus, if you typically drive over many small "stutter-bumps" (quickly), the shock many oscillate more frequently than with the stock springs. Put another way: if the 1st 10% of travel is softer than stock, and you use this 10% most of the time, the overall effect is similar to having softer springs.
However, I don't think this is the case for 99% of normal driving.