Now, I'm working onRight now, I'm studying for final exams, so I cadon't have time to read a book or watch a movie at all. Right now, I'm studying for final exams, so I don't have time to read a book or watch a movie.

Your sentence is grammatically correct, but sounds stiff. For example, "studying for exams" is more concise and tells the reader the same thing as "working on studying for final exams." (Unless you are not actually studying but working on studying itself, like if you are building up motivation/buying materials in order to study or improving your studying methods.)

I'll read and watch a lot during February and March, thanks to my spring vacation. I'll read and watch a lot during February and March, thanks to my spring vacation.

Please tell me your favorite one. Please tell me your favorite one.

I might write: "Please tell me your favorite book or movie." since it's clearer and using "one" here sounds slightly unnatural compared to just saying "book."