Some questions

Hi there.

I had some questions during the Team evaluation.

1. I know I can invite people to the channel, and I can set the arbitration flag to inhibit members in the channel to post messages, to treat as a billboard. But can I add people in my channel directly, not invite(because they may miss the notification to add to my channel)? So I can broadcast my message effectively.
2. In the basic(or free) edition, are there any conditions we would lose our posted messages or attachments?
3. Is there a 3rd party module to let us send messages to notify our users by LINE messages or WeChat messages?

Thanks in advance.