Minimum games played by everyone: 25, so the ratings of players should be pretty accurate, so there is a good chance of a fair and fun tournament!
Groups of 6, with 3 progressing, should mean a small number of simultaneous games, but a fierce battle to make it through. It'll start with 8 groups of 6, then it'll go to 4 groups of 6, it'll come to 2 groups of 6, and finally 1 group of 6, so each round will be more and more closely fought.
No vacation: it'll stop one or two people holding everybody up. If you're on holiday, find an internet café every 3 days.
I hope you have a good tournament!