Coincidentally, I am in the same boat as Lea-Ann. I have an established site with LifterLMS-based courses and memberships via WooCommerce Subscriptions (as well as offering more traditional eCommerce too).
I have a closed Facebook group as one of my membership benefit but a reasonable percentage don’t use Facebook (my membership has a large number of older folks). I have been very interested in moving to a forum and away from the Facebook group, but it’s a change I want to assess and manage very carefully.
I have installed Discourse on a Vultr VPS yesterday, as a subdomain. I have installed the SSO plugin too.
A part of this will be making sure that there’s a consistent user experience. So now I am actively researching my Discourse design (currently looking at themes and theme components). Like the other two posters, I have a real desire to see alternative designs to spark some inspiration.