Not sure how much lighter (if any) a 3.8 front end is. Going one step up to sportline would be a more conservative and probably a better ride.
On my Mustang, I did the Eibach sports and loved them for the street. It wasnt till I got more into corner-carving that I went for more spring.
Stock (on my 1989) is like 420-540#.
Eibach were 450-580# (+10% roughly)
Then went to 650# linear rate, and that was stiff.
Now I run 450# coilovers, which is about 2-1/2 times the rating!
Caster camber plates are only necessary if you cannt get an alignment and get the tires to wear evenly. IMOHO, you are better off getting them anyways, and make it easier on the alignment shop to get it right, versus paying for 2 alignments after you get the cc plates.
Isolators are just to prevent metal-metal (spring/seat) rubbing and squealing. No biggie. Use whatever you had on the car and transfer it. In the rears, there may be a hollow tube up the center of the coil, reuse that too.