1&2. Is around 270-300 rwtq enough for you? Todd's been able to achieve that on their 325i test mule with stage 2 kit.
It depends what you want. The M20 turbo is a little more "peaky" than the m30 turbo, simply due to motor differences. The m30 has really nice mid-range torque stock, so it has really meaty mid-range torque characteristics with a turbo. The m20 likes to rev, making most of its power high in the rpm range, and keeps those same characteristics with a turbo attached.
3. If your goal is maximum power, then yes, do the m30 swap first (or in conjunction with the turbo swap). You can make enough power to embarass a stock M5 with an M20 turbo though. Like I said, it would depend what your ultimate goal is.
Jeremy
PS- Nice looking car, needs some bigger wheels on there though.
