15 minutes 720p 23.976fps would be roughly 5 GBs, I'd say. We're talking somewhat bigger than lagarith but somewhat smaller than huffyuv. What really is nice is that it is ridiculously fast at decoding, so it's perfect for editing purposes.
Compressing audio... uhm... if you don't have to do anything to it, I'd say you should avoid recompressing the audio. If you do, then I guess you can just load both audio and video together by using FFCopyrightInfringement (not trolling, this function really exists and comes with the amvapp) and then normalizing it and saving it as a wav from virtualdub.