Can I just point out one thing, Alpina are not Tuners in the common sense of the word, they are an independent manufacturer, and produce a ltd number of extremely high quality (exceeds BMW's own std's) vehicles, listed as their own cars. You can't buy a 'kit' from Alpina to tune your engine, or the suspension items seperatly (you can get suspension some items, but not all), & they have to be fitted at a dealer (BMW) as a complete package and will then be listed as an Alpina with it's own revised chassis number etc, i'd plaque etc. You will be able to get the wheels, badges, bodykits etc, as these are purely cosmetic. They are the gold standard that others try to attain to, but never quite get there (although Schnitzer are not that far behind)
The MINI has been investigated, they have several 'S' engines on test, looking at how to improve on this. If it gets released, expect excellent suspension alterations, and an engine that will surpass BMW's own 163 supercharged item (it may well retain the supercharger, but it will not have a turbo). Look at 200+bhp and on average £5/8k on top of the list price of the std 'S' dependent on options/packages fitted.
On the K&N front, on other performance BMW's (i.e M3 and M5) the installation of a K&N has shown to upset the sensors that are installed within the Inj System, making the car run too lean, M5's especially, so wether this could have the same affect on the MINI, I don't know..
The JC works kit is sold as a complete item, as it has modifications that allow for this sort of thing.
Hope this helps