Couple of things to consider...
In regards to brakes, I thought stock brakes were suicide on wheels too, while others thought they were 'great'... but either these people didn't drive some better cars or well I just don't know. I've had my car now for three years and well let me say a few things. Also keep in mind I have no ABS (and well after you get better at it honestly I prefer a non abs car but its not for the light hearted):
If you do keep stock brakes here's a few things to check. Check that your calipers are not seized, replace the old rotors (should be cheap) most especially replace the brake fluid with some nice dot4 or better (stay away from silicone stuff), and most importantly replace the brake pads that might be used up. hawk HPS pads should be descent for DD. Track.. don't even think about it, even my HP+ pads on blank 300zx rotors manage to be faded but they are after all for autox... And honestly you're scaring me with how you talk to even think about track time yet hehe.
I upgraded to aluminum 300zx brakes front and rear almost immediately, stainless steel lines, bigger MC, better fluid (ran motul's stuff but I kind of don't like it I tried a few different things). I first ran some ebc red stuff pads and really disliked them (front) while HPS rear... that shit sucked... then I went to Hawk HP+ pads in the front.. that's what I currently have on the car as well... the car is awesome except that HP+ pads have an anoying on/off feeling... at higher speeds with sudden instant stops its okay, but at lower speeds its a sudden bump, bump, crappy crappy CRAPPY modulation, no good in my opinion. I've tried a few different setups as well, but overall I wanted something better. If I were to stay with 300zx brakes I would have went with BHP CR6 pads... I crave that pad...
I realized all the money spent on used 300zx stuff was a waste of money (in my opinion) so recently for my next car rebuild I got myself arizona z car willwood brakes 6pot fronts and 4 pot rears... can't quite comment on it yet as my car is parked waiting for it's next overhaul.
In my opinion 300zx alum brakes should have been stock to begin with.. and surely enough they are on later s14 and s15 Japanese models... Given good pads and brake fluid 300zx are plenty for track, daily, etc... if you want more extreme setups you gotta pay and you probably won't even need them unless you drive on track or like a maniac or well.. you just enjoy to have a car feel that is superior but thats why expensive cars are well.. expensive, don't get too carried away. Like I said if I were to stay with 300zx brakes I'd get some BHP CR6 pads...
These are my opinions based on my limited experiences...
In regards to dampers, well... save yourself the money and build a koni yellow with ground control coilover setup instead of all the chinese/taiwanese or even japanese coilovers out there. Tein he flex or whatever they are called are descent i've driven it, but I still think its ultimately crap, it just feels.. i dont know... its just crap at the end of the day and you won't know unless you've driven in something else. Aanything else I wouldn't bother afterwards honestly. MR, Stance, Godspeed (lol), whatever's out there, all the same shit. If I were to rethink my car build path I would have gone with Koni Yellows + GC coilover setup to begin. Above that the more extreme stuff is things like Koni 86xx but that's something probably not for you yet. Above that well you gotta pay SERIOUS dollars and again that is absolutely not necessary unless you're a track freak (I would think anyways).
If I were you I'd just get 300zx front and rear brakes, replace the brake lines as they may be damaged or just plain old and the rubber stuff sucks for pedal feel, good pads (Bhp CR6 hint hint), good brake fluid (they sell some nice fluid too I am going to try soon), and for coilovers build a koni yellow GC setup believe me it won't dissapoint... Don't fall for the 'they are soft/not stiff' or not 'jdm tyte' crap. Being rock hard doesn't mean shit, it just means having a car that's rock hard literally rock crap. The purpose of dampers is to ABSORB the bumps, the irregularities, etc... it's just that the majority has been brainwashed (myself included initially) that harder is better (drift crowd, etc...)
Edit: Also something no one mentioned since you asked 'what are some good
suspensions' lol uhm... speaking of suspension, you could also dish out money on arm replacments...SPL, peakperformance>everything else>ebay haha. Don't go with polyurethane stuff go straight to heim joint stuff. I didn't realize polyurethane stuff has to be greased/lubricated all the time... plus something I recently learned, it causes increased friction which is not good for the work of the suspension... I wish I just went to heim jointed stuff from the start...
In my opinion however again, I think this might be a little over your head. I would rather sort your car out first that it runs okay... you might have a busted car in many respects (fixes here and there) causing your car to feel not okay.
Also keep one thing in mind... a 240 is a 20 some year old car with 20 some year old technology. It's a good car, but don't expect it to be as good as say a new 350z, or m3 or whatever, you have to spend the money to make the car faster/better in feel/etc... some people don't realize that. Also more than anything else... DONT cheapen out.. you WILL DEFINETELY pay more in the long run. I learned the hard way
