> The body font should read well when printed at 12/18.

Why this exact size/linespacing?

hhp

The University regulations recommend (but do not require) the use of a 12 pt font, with a "spacing between the lines" of approx. 8 mm.
In practice, however, most students are using 12 pt with 1.5-fold line spacing, i.e. 12/18. I guess that depending on the font choice, it would be okay to use a different spacing, as long as the visual appearance of the spacing is similar to Times New Roman set in 12/18.

Times is small on the body, so 12 makes sense. It's good
to know though that you can choose a smaller size if the
font warrants that (meaning you're far less restricted in
terms of font choice).

Concerning linespacing, 1.5 is generally a bit much, unless
your lines have to span the width of a letter-size/A4 page,
which is not advisable. Also note that the ideal linespacing
does depend on the font (mostly its x-height).

hhp

Have you had a look at Skolar? I've never used it, but I've wanted a copy for a long time - sadly it is outside my student price range.

http://www.type-together.com/Skolar

Your requirement of Greek in both sorts narrows the choice down a little bit.

What about Parachute fonts?
Centro Serif Pro and Centro Sans Pro might be a possibility.

Related:
http://typophile.com/node/82845
http://typophile.com/node/88187
http://typophile.com/node/74267

Maybe related:
http://typophile.com/node/89876
Problem with capital letters. Does this apply to your work? Several approaches are considered.

Thank you all very much for your helpful responses.

I am particularly inclined towards using Skolar as the font for body text. In terms of capital letters, likely I will use full caps for abbreviations (rather than small caps), as this is standard in most science publications and people in the field are used to it. Personally, I would however prefer small caps.

Do you have any recommendations (or can refer me to a related post) on which heading fonts would work well with Skolar?