Well, if you really want good handling and are planning on spending $3000 for good suspension pieces, ditch the 18 x 9.5" wheels, they'll undermine the perfection of the rest of the suspension set up.. The extra unsprung weight from such huge wheels will definitely hamper performance, cornering, nimbleness, etc. Not to mention such heavy wheels place a lot of stress on your wheel bearings and will cause you to brake worse as well. Wheel weights make a big difference. And even if you can find a lightweight 18 x 9.5" wheels, the tires will undoubtedly be extremely heavy. Why do you want the 18's? For looks?
I just sold my 17" x 8" 5zigen typhoons for 15" x 7" Work 3 piece wheels--and I have plenty of power to motivate heavy wheels. Switching from the 17" heavy 5zigens to my stock 15" alloys was night and day--the car was much more responsive, handled a lot better, felt a lot quicker, and a helluva lot less sluggish.
I think 17" is plenty big, and a 17" x 8" or 17" x 8.5" (or even a 16" x 9") will be a lot lighter than 18's. If your car is 5 lug, get 17" SSR Comps....they're extremely light, albeit expensive.
I don't mean to bash your idea about the RB25DET, but I'm sure you realize it weighs 180 pounds more than a KA--it'll make the car handle quite a bit differently, with the weight bias of a FWD car just about.
Anyway, another budget minded setup:Tokico BluesEibach ProlinesS/T anti-sway bars f/rPilot front strut bracecusco rear strut bracelightweight 15" wheels all around with grippy Dunlop SP Sport 8000's
I also have heard good things about the Cusco RXB (rear cross brace)> It's supposed to stiffen up the middle of the chasis quite a bit... but with $3k, why not a bolt in roll cage
If I did the shocks/springs myself, (they came on the car) I would have done KYB AGX/Whiteline--they're adjustable, and very high quality...
Anyway, my $.02
Marc