I have a non-fiction book idea that would frequently use quotes/reviews from a specific author. Would I need to get that author's permission to quote him/her, and to base the entire book on these quotes?
Proviso: I am not a lawyer.
Here's a good article on Fair Use; it might answer your question.
You say you'd like to use many quotes from the same author; if you are writing a critique of the author's work, or a biography of him, or some similar piece about the author which you are backing up using the quotes - then you're on pretty safe ground. If, on the other hand, you're using the quotes as content - e.g., "Quotes About Literature" or "Shakespeare's Greatest Zingers," that's a much bigger deal. Something in the middle - making use quotes from the author about the particular topic of your book - is a hazier area; the key consideration is whether reading your book might serve in any way as a substitute for reading the author's work.
Similarly, short quotes are generally not a big problem; you mention "reviews", which are probably a problem. A review is generally a complete, publishable, stand-alone work; reproducing it in its entirety would infringe upon the author's copyright. If you want to say "As Roger Ebert says of the last Harry Potter film: 'it's apparent again in this film that the three leads are upstaged by the supporting characters'", or the summary "Roger Ebert gives the new Potter film 3.5 stars", then you are fine. But you can't reprint the whole review.
I'd ask. If you're not using the quotes to misrepresent the author or show the author in a negative light, I can't see why the person would say no. And I'm not sure where Fair Use ends and Infringement begins in terms of copyright.
Besides, if this person is doing a lot of your heavy lifting, it would be courteous to get the person's permission to be linked with you (or at least to give the person a heads-up).
Assuming that the quotes are coming from the author's works, you would not have to obtain the author's permission. However, you should attribute the quotes to the author and identify the source. Whether you do this as footnotes or as a disclaimer/notice at the beginning of the book would depend on how many quotes and how many sources you are using. If you are going to take all your quotes form a single book, then a notice at the beginning of the book should be sufficient. However, if you are using multiple books or articles by the same author, then you would want to identify each source by title and page.