The word "nothing" in the play's title has always been the subject of speculation. No one knows if Shakespeare chose the word "nothing" with the intention of being ambiguous. In Elizabethan common dialect, "nothing" was pronounced much like "noting," thus allowing the word to be a homonym (a sound-alike word) with four totally different meanings:
nothing (as in present parlance): not anything, zero, zilch, nada
nothing: In Shakespeare's time, "thing" and "nothing" ("nothing") were slang words for referring to a sexual organ; thus phrases with the word "nothing" sometimes had sexual or erotic connotations
noting: writing musical notes
noting: observing, overhearing, perceiving
Note how many key events in the play reflect the last meaning above — overhearing or observing.
Benedick overhears a conversation that informs him that Beatrice is in love with him (Act II, Scene 3). Beatrice overhears a conversation that informs her that Benedick is in love with her (Act III, Scene 1). The watchmen overhear a conversation in which Borachio tells Conrad about faking the scene at the window of Hero's room (Act III, Scene 3).
Antonio reports (incorrectly) to Leonato about an overheard conversation between Don Pedro and Claudio (Act I, Scene 2). Borachio reports (correctly) the same conversation to Don John, leading him to suggest how to use the information for their own purposes (Act I, Scene 3). Don John places Claudio and Don Pedro where they can overhear the mock love scene at the window of Hero's room (between Scenes 2 and 3 of Act III).
Another extended scene involving noting is the dancing sequence in Act II, Scene 1. Most of the characters are masked, allowing them to observe others surreptitiously, themselves hidden (un-notable) behind their masks. In the same scene, the audience itself is allowed to overhear snatches of conversation between pairs of characters not sure about the identity of one another.
All threads of the plot and subplots are intertwined with instances of noting — their planning, their execution, and their consequences. So indeed the story is Much Ado About Nothing.
