Yes, The gases are released throught the wastegate before it its the turbo. There is no minimum boost since you have to go through 1lb to get to 5 and 10lbs of boost.

The difference in the WG isn't only the spring, but the size of the opening on the WG. You can think that at 25 lbs on a T77 is flowing LOTS of air. Once pressure reaches 25lbs the air going through the manifold need to maintain spool but not increase it. The wastegate opens and allows that air to go via the dumptube.

If your WG is to small, when it opens (or doesn't open all the way or is to small for the amount of air needing to be relased), it will not allow the correct amount of air out the tube. This will send the "extra" exhaust air through the turbine causing a boost creep.

The good thing is that 38mm will work fine on your B16. If you need more you can put a stronger spring on it and you'll have plent of waste available for a B16.

O... and it usually knows how much gasses are needed to go to the turbine instead of WG by the boost preasure.

This is only my understanding, I'm no expert.