A couple of tips in this to help you make more from LinkedIn groups. The theory is fine, but the user experience of LinkedIn groups is quite different. Since they changed the look, feel and layout, engagement in groups has fallen off a cliff.
However, I have two groups on LinkedIn - one with around 7,000 members and the other with 24,000 and I continue to invest time in them because it will pay dividends in the long run because of the Community aspect.
Good news though, LinkedIn has announced that they will soon be upgrading groups, and one of the key ways they'll be doing that is by posting group content into the home page news feed.
https://www.businessnewsdaily.com/10719-tips-tricks-linkedin-groups.html