I not sure multisite needs to be mentioned here 
or maybe the adv config group could come with a warning, search meta ! For instance this post is very useful pros-and-cons-of-a-multisite-installation .
About the Sending Bulk User Invites, I tend now to use multiple-use-invite-links, perhaps mention both topics?
I think I’d set Set up Reply via Email Support 
in the advanced setup group (since I still haven’t done it 
) and straightforward-direct-delivery-incoming-mail is probably worth mentioning but maybe in the adv. config group, because … well… email 
.
The contrib group seems a bit empty, perhaps something theme or component related would be nice, such as developer-s-guide-to-discourse-themes , designers-guide-to-discourse-themes and beginners-guide-to-using-theme-creator-and-theme-cli-to-start-building-a-discourse-theme