In reply to designing a face from small -> up:
IIRC Frode (http://typophile.com/user/17101) did some experiments along these lines, mostly to optimise hints.
I still am, but somewhat different.
Unless you are the only user, and reader, there’s no way to be sure of the exact output size. What I am doing is optimizing my fonts for a small range of sizes on systems that do not use hinting. Whoever told us OSX can do all the heavy lifting on its own was a fool. Even the Quartz rendering engine involves some degree of math “magic”, causing diacritica and base glyph crashes, alignment errors, filling in of tight contours, heavier diagonals &c. I spend a lot of time getting all that right, simplify A LOT of details, and then -- then I hint.
And I optimize so that I need as few hints as possible.
