lots of ideas. BMW Parts and BMW Accessories | Bavarian Autosport
Google, Ireland engineering, BMP motorsports, Downing Atlanta Supercharger, Dinan....
They will all sell you things to put on the car.
Turbo, google will be your best friend, read about every turbo swap anyone has ever done before you start and budget way over for it.
The DA supercharger would be a better bet, less hp in the end, but proven performance and you might be able to find a mechanic that has put on one before depending on where you live.
I had a 95 318i, it already had a chip and cai in it when I got it, so I put spring/shocks for handling. Would eventuall have done sway bars, but not much else.