Hello again Ivor!
1) The initial Epitaph story seem like its going to be a prequel, here's part of my summary of an interview the booted dudes guys did with the Booted Dudes podcast.
2) I don't think this has been revealed one way or the other yet? We'll need to wait for more previews. Sorry if somebody at Pinebox has confirmed this one way or the other and I missed it. I'm being a bit cautious on this one Ivor as I don't want to accidentally break the playtesting nondisclosure agreement.
3) The booted dudes interview I link to above gives you some quick initial information all in one place. There's a summary of the interview that I wrote up if you don't have time for the full podcast (which is worth a listen and has more details). I and others can try to help out in this thread if you need more.
4) I don't know about Origins, sorry. There are tournament plans for Gen Con.
As to which card set to buy, you've got good timing on that question! I just wrote a big guide to this topic, link below. It has some suggestions for some good Fourth Ring specific sets and also notes which sets introduce Eagle Wardens/108 Righteous Bandits/Miracles so you can avoid these/pick them up if you're keen on adding them or just focusing on the stuff you already have.
I know you're keen on your monsters and Fourth Ring, so Faith and Fear would be a great pick-up for you as it has a non-unique Fourth Ring Abomination and an excellent starting Fourth Ring huckster (links below).