Yes, this unit does include GPS. Humminbird HELIX 7 G3 - CHIRP MEGA DI Fishfinder/GPS Combo w/ Transom Mount Transducer
I doubt it, Japanese fish are to stealthy.
G2N is 2d generation with networking capability. G3 is 3d generation without networking, G3N with networking…
I have used my MEGA G-3 unit with the transducer that came with my G-2 unit. It works fine but needs to be identified in the settings. I have also used it with he transducer that came with the MEGA G-3 unit. It has what they call MEGA capabilities which do improve the image quality some.