There will be 6 main characters, Robin (Dick Grayson), Artemis, Aqualad (Jackson Hyde), Miss Martian, Superboy, Kid Flash (Wally West). There will be two other regulars added throughout the season.
There will be other characters in the series, according to an article from s8.com will have featured 135 supporting characters from the DCU by episode 16.
The Justice League will be a big feature in the series, especially Batman who will be working as the group's general who chooses the team and assigns missions. Superman, Flash, Martian Manhunter, Aquaman and Green Lantern shall also feature prominently as mentors for the group. Captain Marvel will have a big role, as his alter ego is Billy Batson a 10 year old boy. Also Black Canary will have a large feature even though she isn't a direct mentor. Roy Harper will feature, graduating from Speedy to Red Arrow. Garth and Arrowette will also feature. Wonder Woman will appear in alter episodes due to being prohibited during early stages of production.
This show should hopefully be a smash hit, and starts airing in November!