First of all, let me say that I love the idea and it has everything to work...

So, the team size doesn't really matter to me, we can even have more/different team up´s with different amount of team members, so that´s for you to decide.
To me, the most important factor is the time of the tournaments, so I agree with different times/days favoring a different time zone in the world each time. To me, the ideal time would be 22:00 CET on any day of the week.

When it comes to the pre-tournament, I would like to claim an invite already :D
And the preferable time to play would be the same as mentioned above. But the ideal is to find the most suitable time considering all suggestions (not many so far...)