Fonts: I've used Times Roman (11 pt) for years now (except on scripts, where courier is still the norm for reasons related to screen time calculation) and nobody has ever complained. I rarely see Courier these days: for a print-out intended primarily for reading - as opposed to copy editing - it typically uses up way more paper than necessary and produces very bulky manuscripts.
You don't have to use Times Roman. Book Antiqua and Bookman Old Style are also fine, especially if you're writing something a little bit gothic. Just make sure it's very clear and very readable.
In general I would say:
a. stick to 'true' fonts; so there won't be compatibility issues.
b. avoid fancy fonts, even for title pages.
c. be careful to keep margins wide enough that the text does not run to more characters/words per line than you would see in a normal paperback (long lines of type are hard on the eye).
d. Use 1.5 line spacing. Double spacing is really only desirable for a copy editor's copy. For a reading copy it's needlessly spaced out, in my view.
These days manuscripts are invariably delivered electronically. A print-out is a courtesy, and may not even be wanted. That means the reader can switch to double spacing at the flick of a mouse. He or she can change the font too, for that matter. That said, if you are submitting material for preliminary assessment, keep everything as plain as possible.
http://thiswriterstale.blogspot.com/