why must it be 3v3v3v3? 3v3 is perfectly balanced, isn't a feeding off the weaker teams contest, and would actually determine which team has superior teamwork & micro. I talked with Konvict a week or so back he said it would be 3v3, to eliminated imbalance, targetting, and feeding issues.
Also a 3v3v3v3 format wouldn't make sense if the number of participants weren't a multiple of 4, and with the same amount of teams from each clan/teams to prevent targeting and teaming up. even then, just the mere coincidence of targetting makes 3v3v3v3 imbalanced for competitive play, but i'll leave that for another day/topic =)
as far as rules, i agree with the 2 set rules of normal mode and every player must get a hero. everything else should be available to use.