We've always had this issue. The problem is too many (dbag) players will pretend to be new, and they aren't. It's happened before. People even do it now w/out the tourney. We've done non-pro tournaments, but it seems tier 3 and below don't have interest, as they are less competitive people imo.
No max number of people can join. GOW is what everyone feels most comfortable playing. Many top players won't play otherwise. Duda has hosted many of these other tournaments before with some success but not close to a big GOW tourney success. If only 2-3 of the top 10 players play, it's still just destruction until semi-finals. GOW has more people watching as well. U8 can get over 100 players on his stream.
Usually, you'll see players practicing the week of. I haven't seen anyone. Not sure how well this one is going to work out.