those mods sound like good ones.
i have a 63mm exhaust. any upgrade on pipe size will help performance, but your best bet is to go with a 76mm. this is a very common size to upgrade to. when you see it on the car the piping looks mahoosive, but thats a good thing. it allows the turbo to expel exhaust more efficiently, and results in a gain of power.
new mags - awesome. the standard ones are definitely way too small. n1smo200sx has 18's and it look downright fantastic.
apparently the s14 turbo outlet is slightly larger, and this goes hand in hand with the larger zorst. another good thing, but the gains might be very small. but then again, every little bit helps.
i'm not so sure about cutting the bottom of the airbox off. this might actually reduce your output hey, but again this is a contentious issue. i have a cone filter, and i'm not even sure this helps anything. remember the filter is on the hot side of the engine, and removing parts of the airbox might help to suck hot air into the turbo. not good for performance, but i know it sounds lekka.
FMIC - very good mod to do. but dont go mad, get a size that matches your setup. while you're doing this mod, its also easy to put in a BOV. some poophols call it a dump valve. sounds awesome, and helps prolong the life of the turbo by eliminating backpressure on the blades when you close the throttle.
you dont need an adjustable actuator to get to 0.8 bar boost. a simple boost controller will do it, but the best would be some form of electronic boost control. this is however, quite expensive. remember that anything over 0.8 bar on a stock turbo will see the turbo operating out of its efficiency range and will just blow hot air into your system, without increasing your power much at all. you'll get heat soak all the time, and your turbo wont last very long at all.
as for suspension - this is one part where you can seriously increase the enjoyment you get from your car. lowering the car helps looks yes, but can help handling too, if you get decent springs. i would also suggest polyurethane suspension bushes. the best kit to get is from energy suspension in the states. its the cheapest and most complete kit you will find, and this seriously will increase the handling of the car, specially in conjunction with bigger mags and better tires.
now get out there and go do it.
DO IT!!!