#1 - no you do not need that - you can just run the intake manifold pressure line to the IP ALDA. The switch is an overboost protection switch that cuts the boost signal down to the ALDA if the intake pressure reaches 16 psi (or somewhere around there). I would recommend running the engine and "teeing" off of this line to ascertain how much boost you are getting with the existing wastegate setting. You can safely run up to around 12 or 13 psi. I have bypassed this switch on my 300D but have confirmed the wastegate setting. The only issue is if the wastegate fails closed then you can mess up the engine if the pressure goes over 16 psi although you should be in for the ride of your life for a few minutes
. Personally, I would not worry too much about it.
#3 - Get rid of the Bowden cable stuff - you don't need it anymore.