Suspension's where it's at for autox, it doesn't matter how much power you have. I've been beaten by guys with 84 jetta diesels. (60hp?) It's all handling and driving. Somehow autox defies real life driving.
I think that conversion will take you about a year to do. No joke. You'll be in a whole new area when it comes to needing TIS schematics from BMW on that motor that aren't readily available to the public. You'll also need the DME and the engine harness so that's about another 2-3K in parts right there.
If you want a lot of power get an eagle talon tsi. They're fast as hell and cheap.