I can only address the audio upgrade. Posted a lot about it on the Bimmerfest forum. Upgraded one step at a time: speakers, then ghost subs, then Bimmertech amp. Each step improved sound dramatically. Can't say which upgrade was best, but I wasn't happy until the whole deal was complete. If you hate the stock stereo as much as I, have $2k to spare and don't mind spending several hours installing everything yourself, then go for it. I'm more than happy. The biggest issue encountered was Bimmertech had no custom amp mounting bracket for the car. I provided pics and measurements and it looks like I'll have a bracket soon.
Forum people greatly prefer the jb4 to Dinan , probably due to cost, mostly. It's my impression the Dinan software also modifies the TCU, so maybe you won't need the Alpina flash.
From day one, everyone has raved about the alpina flash. I read a lot and found the necessary software, but the more I read, the less clear the process seemed, so I decided to live without it. I love the smoothness of the transmission around town, and that's most of my driving. I also have a tendency to not get things quite right the first time. That could lead to catastrophic consequences. There is the option of paying someone to code your car remotely. Prices are reasonable. However, if the dealer has to do anything to your car's software, any custom settings may be wiped out. My car needed complete re-programming to clear an error a while back, so was glad I hadn't paid for custom coding.
Enjoy the ride
