Building the Twin Adder setup isn't overly difficult, or buying an off the shelf setup and keeping the */C isn't hard either (at least for the S2/3).
The hard part comes in when you need regulate boost. There are a few different ways to do this and the easiest involves using the stock BBV setup. But you will extremely restricted on boost levels, you'll never be above 20lbs(I don't remember the exact number, but IIRC its ~14lbs).
ZZP/Stamma can build the boost controller for you, but IIRC it was very pricey.
Bottom line, for ease and reliabilty run a single turbo. 7lbs (non I/C) on an L36 bottom makes for an extremely reliable quick car.