That seems pretty far out to be at 3000. If you are under the class B the aircraft should be a 200kts not 250. And the controllers are supposed to tell you that you are under class B(FARAIM ref)....but they don't.

I would go with a transponder. You'll see the commercial airliners doing quite a few TCAS warning maneuvers and if ATC gets enough of them they will stop vectoring so low in that sector.

Pilots may not be head down but that terminal area is BUSY. And although we do look outside, it is our busiest time in the entire flight.