I would use a boolean modifier set to union, apply it and use the sculpt mode to smooth the intersection. This will ruin the topology so if you want to animate it you will need to retopologize.
Alternatively you could merge the vertices as was suggested, or just keep them as two separate meshes and use clothing or necklace to hide the neck seam.
Subs are your friend. I studied Japanese got over a year, but most of my vocabulary came from animes and games. Try to find some Korean shows that might interest you. If you are into games, some mmos have Korean voice overs. Korean alphabet is simpler too so it should be a lot more effective for you. Still, if you need to practice reading Koreans make a lot of good webtoons. Finding originals may be a bit harder but give it a try.