As the group is growing, expect that there will be trolls or scammers that will try to explore the channel.
If everyone is free to join then its likely to happen. Thats why I dont really join in group about predictions because you cant get the idea that you're looking for since scammers are present.
It is true, better look for prediction threads in this forum in the gambling discussion boards. There are so many good insights already that you can get from the members here. For me, that's more than enough. But maybe, the OP has other goals for his group later on.
If op is true to his intention then its fine to create his own betting group to share ideas. But as you've said, this forum is also enough for me to fill my mind with the information that I need so its not necessary to join in betting group.