2) The usual, don't post for another character that isn't yours. Exceptions include if you have permission from the person who plays that character or if that character has no player. However, please keep in mind that that character should still be acting within their established classical limits. That means Cronus can't just suddenly appear and crush all the godlings down. By that same token, as long as you don't have a completely virginal character, establishing new relationships that were never included in the original mythology wouldn't be horrendous. Just try to be sure it doesn't completely violate some known fact about the characters involved.
3) Posting at least once a week for each character would be greatly desired. However, I'm not of the mind to sit there calculating each time you've posted, so it's really just a suggestion and preference. If you're going to be away for a while or unable to post, it would really rock my socks if you'd let us know via this community.
Finally, chipmunkkc, since this was really your idea, if you have anything else to add, please do (and I did make you a co-mod of the community). And if you have any issues with the above general rules, let me know, and I'll fix it.