It works online. I just loaded it and it's playing right now on the void server. But, that still doesn't answer your question about max filesize. I'll do some research.
Edit: I don't know if it's still the case. but as of Beta1d, the max filesize supported by servers was 1MB. This was told by xbx (a Nadeo guy) in the private beta forum.
It could be more or less now. If you could compile a few maps with sizes just under and over 1 MB... we could test it out and know for sure.