Everyone who is there gets to play! The tournament will be run with Swiss, meaning everyone plays 6/7 rounds. As Master Registration is 11:30 AM - 12:30 PM, you should get there between that time or maybe even a bit earlier just to make sure everything works out properly.
im gonna try to make it to worlds dis year. I only ever tried going to a vgc once several years ago and on my second battle i got sheer colded 3 times in a row and criticaled for the loss. Now im gonna make sure that doesnt happen again.
Last year was my first year and I made it to the top 64, one round from cuts, all because of haxed out fissure. Plus my mom actually decided to take me since she thought it would be a fun birthday trip.
Basically, if you don't use RNG'd mons you're putting yourself at a disadvantage before the tournament even starts. I highly recommend either learning to do it or finding someone nice enough to do it for you.