A good starting point is to adjust the rod length (I assume you have an internal wastegate similar to stock).... so that you just have to pull the rod about 1/8" to get it on the pin of the wastegate puck..... that will be about the lowest boost that wastegate can be set at.... any additional shortening of the rod raises the boost pressure.
Where you tapped in for your boost gauge is fine..... just make sure you have no broken vacuum hoses and your wastegate is adjusted properly.....
HTH