you will get maybe 200hp out of it after dropping a lot of money (thousands) on any and all NA mods you can get (headers, exhaust, cams, etc). The only way to get a lot more power is a supercharger which will get you ~100hp and put you at ~280hp at the crank...that's less power than most 6 cylinder family sedans today and that's after dropping $5k on a supercharger to go into an $8k car.
If you want power or go fast, this is not the car for you. Don't invest a ton of money into an old car like an E46 unless you want to race it or track it and in which case you should be looking for a 330 and ripping out as much weight as you can instead of adding power. If you want a slower car with great handling and decent looks then you've found it.