You see a lot of "I want to turbo my E36 Mxx engine" or "can I add a mini supercharger to my 316" on the forum which is all well and good but most of the time it is just a pipe dream.
The in reality the effort involved is huge, it is not a case of slapping a bit of stainless pipe on two metal flanges, the exhaust manifold needs to tuned, as does the induction side. If it is not you end up driving around in misery with a car that has great flat spots and unpredictable power bands. Once you start tinkering at this level you need to be able to adjust the engine map to hone the right characteristics.
The best thing to do is sell the 323i buy a 328i, remap it and put some basic mods that will squeaze another 10hp out of it and save a lot of pain