Both ways should work just fine. It doesn't matter if you are not in the top20 monthly as long as there is some seeding before teams will be randomized. Every team starts still from the same line, but this way there won't be all top15 teams in one group (A) and that way teams 9-15 would be out of playoffs as they might have been able to be #1-2 in other groups (B, C or D). What I'm trying to say, is that I prefer any kind of seeding before groups are made, as long as groups are still equal in the first tournament.
I would also like to play few more games before x-mas, but it is you who knows it best how we should do it. If you feel like you aren't ready with the site before 14th, it's ok to for me to wait. I rather play the games when everything is completely ready than rush. We all should be thankful for you guys, that we will even be having this site.