1. One cut is required but a sawzall makes quick work of it. No welding.
2. Except for the one cut, it is straight-forward to install. Installed it with a friend in his garage in about 30 minutes.
3. It does to me. It sounds great without being obtrusive.
4. I don't. It is just the back box so I don't think it reduces the backpressure that much.
2011 335i xDrive Sedan / 6MT / M-Sport / PPK1