To make that kind of power, talk to ilikebmxbikes. He just did an engine swap to the e92 m3 engine. That's how you add power that's not going to explode our blocks. If you're trying to pump as much as possible out of the 6-er, you're looking at a new turbo setup.
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To end the brake discussion, you'd be selling yourself short with the stock brakes. You need a BBK for cooling and to run true race pads. Stoptech trophy kits are really stellar, but you can also get solid bolt ons from brembo.
You're going to need to redo basically everything on the suspension for your car. Talk to BRRacing or Evolution racewerks for their recommendations as they've both had true 135i race builds.
I'd put a rough cost estimate at 55-60k USD to achieve those sort of goals, with an extra 10k stashed away for a spare engine.