Most readers are comfortable with Times Roman, Garamond, Book Antiqua or similar style. 12 point is most common font size.
Keep in mind that where you position the beginning of each chapter on the
page, and especially font size, will impact the length of the book. This in turn will determine the production cost and thereby the retail cost.
If you are going with one of the POD outfits e.g iUniverse then page count will definitely set the retail pricing.
Good Luck with your project!
C