go to the movies

Which one is correct?
go to the movies (o)
go to movies (o)
go to a movie (o)
go to the movie (o)

go to a theater (o)
go to the theater (o)
go to theaters (o)

see a movie (o)
see movies (x)
see the movie (x)
see the movies (x)
can I use “watch” to replace “see”?

All of those phrases are correct. You can also use ‘watch’.