Keep it SIMPLE. Less is more. Focus on increasing "engagement".
Ask them questions. Have them comment (introduce themselves) and like 3 other people's comments each day. . If THEY comment, THEY will see the content in this group.✅
I am in hundreds of groups and I never see anything anyone posts in these groups because I never comment or post in them. The few that I post in on occasion, are the only ones I see.
So by having them answer a question they can answer, like "What is your name and where are you from?" or even "Post a photo of your favourite hobbie (or pet)." etc. ... then if THEY comment, when YOU post in future, they will actually see it.😉
The content for the challenge should be primarily IN THE VIDEO. You are correct in assuming that less is more. Occasionally it is easier to post a pdf of some resource in group rather than video.
BUT the ONLY reason to have this challenge is just to BOOK a CALL #1.
If they ask ANY questions, say "Great question, let's hop on a call." 🥰🙌
If there is too much info it can be overwhelming and there is less reason for them to "hop on a call."