chicopaddleheads,
There was an annotation originally on the #wiki home page which
stated that a new post could REPLACE the wiki home page.
Do you mean where it says (or said) "Create a page with the title of Home to replace this page"? Note that's _page_ not _post_.
To experiment this was done. So the table of contents which
originally appeared is gone. How can this be UNdone?
Change the name of that page to something other than "Home". The index page that appears by default should return.
What customizations are possible?
Browse through GMF's Wiki for some examples. I replaced the Index page with a Home page that isn't an alphabetical list of the pages (that's available via the Pages button) and instead made a directory that's broken into sections. But all of that is manually written and maintained, not an automatically generated table of contents.
On some of the pages (for example "Composing New Topics and Replies: tips and tricks") I've used the TOC feature to create an automatically maintained TOC for just that page. There is no feature (that I know of) which will generate a list of the pages in your wiki, other than the default Index page or the Pages button.
What's the best way to INTEGRATE a Google Drive? (into any part of
Groups.io)
I don't know about that.
An easy thing is to have a link to it in the wiki, or the group description, or a sticky topic, or the group guidelines, wherever makes sense. But that's not really "integrated".
Shal