tbh, most flash games are mostly the audio, and some images. code doesn't take up much space unless it's particularly complex. so don't be frightened by file sizes.
my submission, for example, was 850kb, and it's a 54-second loop, at 128kbps. you could afford to go slightly lower and not kill your quality too much. most flash games i find sound like they're at 96kbps, which isn't great, but since it's mono it's a lot better sound than you'd get otherwise (even 128kbps stero is only 64kbps per ear, as opposed to mono where it's 128 on both).