There is a great "group buy" for springs, shocks etc all set up for an R33. If you have the cash this would be the way to go.
The shocks/spring are dead easy to remove, jack the car up to remove most of the load on the springs; undo the nuts at the top and the bolt at the bottom, jack it up a bit further and it will fall out.
Repeat in reverse to reassemble.
There are plenty of good front mouns for sale (new and second hand) as a minimum get a GTR unit, or the Hybrid units are quite good. Make sure it includes all pipes and silicon joiners (between $500 and $1000)
Boos t needs to be kept a lot lower than 20psi unless you change the turbo. I wouldnt worry to much about 12psi, but 14psi for any length of time can be a great way to get a new turbo. To help you here make sure you get a good bleed valve and ensure boost dosnt creep too high under load, or better still get an electronic boost controller.
If you want to run 20psi with any turbo you will need to upgrade your fuel asystem as well (pump and injectors)
PS you will need a new ECU to make the most out of your mods. Most people recommend a Power FC, but there are others.
Hope this helps.