This is quite revealing, for Justice League:
1-7 - Original founding members
8-16 - Expanded members
17-21 - Expanded members from "Agendas"
22-26 - Expanded members since "Happy New Years"
Because Cat Grant said Rocket and Zatanna were the newest members, we can probably assume that 26 is the current cap (since Zatanna is 25 and Rocket is 26). Black Lightning is also new, so he's probably 22/23/24. Which means two slots have not been revealed, as much as I want it to be Vixen or Doctor Light, Fire or Ice...I'm betting its Kid Flash and Aqualad.
Now for the team:
There are nine members in season 1 (Dick, Roy-Clone, Connor, Wally, Kaldur, Zatanna, Artemis, Megan, Raquel)
In season 2, we are introduced to Batgirl, Robin (Tim), Lagoon Boy, Beast Boy, Wonder Girl, Blue Beetle, Bumblebee, Mal Duncan... and if you add that, it will be 17!
However, Blue Beetle is 22 (Tim is 20, Beast Boy is 19, Bumblebee is 17)... that means... Five other unknown members are still not shown and or joined/quit during the time skip since there designation numbers are between the original 9's and the latter numbers.
So who could the other five be? Maybe Tula, Garth, Bette Kane, Arrowette, Secret? They all made cameos... but I'm hoping for different members. lol