Our working assumption is that neither the JRs nor SRs will exceed 256, and that the MAs will exceed 512 but won’t exceed 1024. The first round of a single elimination tournament consists of a bunch of byes and enough matches to get the field down to a perfect power of two. This means that the biggest round is round two, and if our assumptions are correct the most seats we will need for the LCQ is 768.
We therefore don’t need a cap. Even if the MAs surprise us and exceed 1024 we can either use open gaming or run the first 2 MAs rounds before starting the other age groups. The JRs and SRs are only going to need 5 rounds to get from >128 but <256 down to 8 and MAs will most likely need 7 rounds to get from >512 but < 1024 to 8.
The other bit of bad information that I want to dispel is that lining up early is a good idea. It isn’t. Getting there about 9:00 when registration starts is plenty early enough. If you tend toward paranoia, get there around 8:30 but please don’t get there before staff arrives at 8:00. Camping out at five in the morning serves no purpose other than to make you tired..