You'll be just fine. The factory Bilstein's are actually complemented by a decent lowering spring if I recall correctly. Either way, I - along with numerous others - am running H&R race springs on the Bilstein's with absolutely no issues.
Me too! I heard the car runs not as smooth once you've lowered them, and I really can't tell a difference at all. Car runs just as smooth as it did before the lower.
DO take the time and gather opinions along with pics from other members, and decide whether or not to keep your iso's in. I have one iso in the back and both in the front. I'm now starting to wish I had either one Iso in front, or none at all. It just gives it that slightly more aggressive look. It's just nice to get it all done right the first time.
Adding the right shocks and struts will get you more at a later time. Maximum Motorsports are a good match. They use HR Race springs in their Cobra shock/strut packages.