Re: to the theatre
In the US, we go to movie theaters. It would be quiet common to ask something like "Which theater are you going to?" in reference to a movie. (Certainly, if someone said only "I'm going to the theater tonight" the first thought would be live entertainment, but once you're talking about movies, theater is still the right word.)
I'm going to see a movie.
We're going to the movies.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.