With those springs and shocks alone there will be a very noticeable difference in the handling of the car.

The Neuspeed STB is really good, but also consider getting a triangulated bar to further improve the stiffness of the chassis...there's the Benen bar and the PasswordJDM bar. They're a bit more pricey but they bolt to the firewall as well as the strut towers to further reduce a bit of flex.

With the sway bar, yeah, putting an ITR rear sway would increase the car's tendancy toward oversteer, but if you get a bigger front sway bar, bigger than the ITR rear, then that should help with the possible oversteer.

Another, slightly more pricey, route to increasing the handling performance of the car would be to get lightweight wheels and better tires. I personally have 15" Falken Hanabi wheels that weigh 11lbs each (I really honestly did notice a difference with the much lighter wheels) and 205-50R15 Falken Ziex ZE 512 tires, and so far my (stock) suspension has bottomed out and given up before those tires have squealed. Decreasing rotating mass in the car is always a quick route to slightly improved acceleration, braking, handling, and even a tiny bit of fuel efficiency.

Hope all this helps some, and of course feel free to ask more questions!