I believe that it all can be combined once the books proper discussion are started. For plot is indeed known (but how well?
), but what lies beyond and out there is also of great interest
My suggestion would be not to be intimidated if some drafts of HoME 5, or letters, or works of Boethius and anything besides show up (and I believe those may come up, just for the look of the thing and to see 'what it would have been like if published in 1940' and 'does Pope look like Tom Bombadil to you' or whatever)
If you find some post boring, skip it, just make sure when contributing your own entry to indicate whom are you answering and on what (by quoting, or addressing people to post (with its number) that you have in mind. It was done before, and quite successfully. The posts that bore you may be full of wonder to some other readers, and, if dealt with in similar way, will not be confusing (I believe) at all.