I understand from your words (unless irony is involved) that you know something about sensors, and that's probably more than myself, as I only know what I learned in games, but, it's not the usual practice to begin with passive sensors and then go to active as needed?
If so, I guess IR band and neutrino would be the main long range ship detectors (though neutrinos can be minimized, as Spinward Flow says, by reducing the power output), while radar, ladar and densiometers (this latter being also passive, but, as I understand, more directional and short ranged) to get a clearer picture and pinpoint...