Your going to have to lower compression in the engine. This can be done with either dished pistons or a thicker head gaskets (pistons are better but more expensive). For high boost your going to need stronger rods, pistons and bearings, and strong head bolts. It would be good to get the block and head machined by a shop to make sure they are in good working order. To tune it the best but pricey route to go would be a stand alone system, its more expensive than a piggy back but you honestly don't want to skimp on this. Do you want to boost with a turbo or super charger?
Go to Bimmerforums.com and just read, read everything you can find. (Don't post a thread asking questions you could find the answers to by searching, they will get pissed)