Honestly, it's not worth the headache to keep the stock ecu and dash display. It's going to be a nightmare to blend the stock ecu setup with the Haltech. Otherwise youll have to hack the nuetral saftey switch and deal with issues relating to anti-theft ignition issues.
Id suggest retrofitting Haltech's digital dash display to the stock location. You'll have to wire the starter direct to a relay and then to the huracan switch. If you do want a key, you can use a universal FM transmitter key for protection that can be wired between.
The factory BCM will function like normal through the mmi.
And the piece at the steering wheel you're referring to is the clockspring. It transmits signals from each button to talk to the bcm for commands by use of (-) negative resistance.