I just did this over the Xmas break. Got the AA drop-in intake, AA Pulley, Turner Test Pipe, and Evolve-R software. This is the definitely the cheapest way to squeeze some more power out of the car. I even ran before and after dynos just to see the gain and there was clearly a power increase.
For the test pipe, there's not much difference, I went with Turner only because I've known and used their product since the e36 days. But it basically just a straight piece of pipe, I don't see much engineering required. Pulley you can do some research, some uses one pulley, custom belt, other has two pulley etc. There's a thread discussion the various manufacture's pulley. I went with AA once again base on my e36 experience with them, and they had a sale going on. Software is once again subjective, but I suspect they are probably all very similiar. Mike Benevo, ESS, and Evolve.
As far as sound goes, on startup its even louder then before, quite annoying (embarassing) actually even with the pre-heat cat sequence deleted, but that crazy rumble goes away in less then a minute. On normal driving & cruising, its a few decibels louder. On hard acceleration, its also a tad louder (which I enjoy).
Overall I really enjoy these mods, my only regret is I wish I had done it sooner. I'm actually 'afraid' of my car again cause its so fast and responsive. Its a hard feeling to explain. Can't wait to take it out to track again with these new mods.
BTW, I would definitely get the software with it, it clears the errors, and it makes the car silky smooth. I use to have a lot of DCT jerks during cold start, low gears. All of this is gone now, plus you gain a few more ponies.