We got info on that today. While 100-ish is a baseline, they will add enough to keep the Council active. If they feel they need more input, they will open apps again during the 1 year term.
All applicants are limited to the 1 year term and have to re-apply again after that year.
This post goes over it. Explains that the goal is keeping it interactive hence the possible re-opening of apps. You never know what life will throw at people during a year!