[OS X Emacs] Using one font and color theme in Aquamacs 1.6

[Art]

I would like to use one fixed-width font and one foreground and background color
everywhere in Aquamacs that I can type text in. I would like these not to change
as I change buffers, buffer types, frames, use modes that I haven't used before.

I have seen many patient responses to a similar question in this list but I am
still not sure how to do it. The wiki posts related to this seem to refer to
older versions of Aquamacs as the menu options no longer appear. It would be
great to make this change in an minimar way without interfering with other
default Aquamacs functionality.

Thanks,
Art.