Most exposition is just two or three scenes, and sometimes it's just half a scene. For example, in The Hobbit, there are just a couple of pages of exposition before Gandalf shows up and invites Bilbo on an adventure.

What is too much exposition?

If the exposition isn't explaining something that is relevant right now, or will be relevant very shortly (as in, like, the next couple pages), and it isn't something that would come up naturally, it's probably too much.

What makes a good exposition?

Exposition needs to feel seamless; that it's either information that emerged naturally, or else something the reader 'noticed' as they were witnessing the story. Great authors subtly mold scenes to make exposition easier, but success rides on their ability to do this without getting caught.