Any time one makes suspension mods it is adviseable to do them incrementally so you can test the results and know what mod is making what changes to the car. And by all means go to a safe spot and test it so you do not get surprised on a street or highway.
Virtually any change will have an impact on the handling of the car that brings out or highlights something else. Essentially everytime you "upgrade" the performance of a part or system associated with handling, there appears a new "weak link". If you are fortunate, it is at an overall level of performance that is higher than where you were before you made the change. But that is not always the case! So, for test purposes, assume you were experiencing a handling problem that manifested itself with a turn at 45mph. You make a change, say your anti sway bars. Don't take the car to 45mph and then make the turn for the first time, especially on a roadway, or you might find yourself on an off road excursion into the trees! Take it slower, and then gradually and in stages take it to 45 mph and beyond. More importantly, do not focus overly on the handling characteristic you just addressed. Be alert to what else the car is doing..because if you did do it right and you are able to go more safely and quickly through the turn than before....it is very likely that something else in the handling package will be reaching its limits and is now going to let you down, and it is not probable that it will wait to happen until you reach 75mph!
Everything in suspension/handling is a balance.
Anti sway bars may be the best "bang for the buck" improvement to overall cornering capability as a first mod. A lot of reputable companies will have worked out a balanced upgrade for both front and back. But there are a lot of other things to do as well. You can make some changes to your tire pressure to fine tune understeer/oversteer, though for a street car that is usually too fine an adjustment to really matter.
Wheels and tires are critical. If you are going to change your wheels then really do some research before you spend your money, and consider the performance implications in addition to the styling. If you want performance results, then lighten up the unsprung weight with lighter forged one piece or MAT performance cast (Enkei) wheels. Widen the contact patch with a wider wheel rim that will accomodate a larger treadwidth tire (I am running a 255mm instead of the stock 225mm and that much additional rubber and lighter weight on all four wheels provides a much crisper and stable turn in response, not to mention braking and acceleration grip. With lighter weight wheels/tires also comes less inertial momentum on the spinning wheel to slow down in braking, or speed up in acceleration. Adjustments to the springs/dampers on cars are also critical and a lot can be done there (there are of course special considerations with air bag ride). Bushings may be replaced with harder urethane compounds, though if you go too hard you can get squeaking from them. Stut tower braces or underbody ladders and braces can reduce chassis flex, further improving handling and diminishing body roll and pitch under hard braking and cornering. But....where are the limits that you are likely to be approaching in the manner you actually use the car. This is not a track beast, and so building in some capabilities that you are never going to encounter make no sense. At some point the noise, vibration and harshness that comes from these changes will be unacceptable to you or your passengers....at what price in comfort are you willing to pay (in addition to the bucks) to get performance? That is very individual, and what I might think is peachy keen you may find to be obnoxiously bumpy.
Bottom line, you can spend just a little money and get some quantum improvements in handling. But be careful and intelligent about it before spending your hard earned dough.