I had the same thought, that that was the best episode so far. I was captivated the entire length, and it was a longer episode, to boot. It was partly so satisfying, I think, because we got a lot of answers. Besides the reveal of William's daughter, we learned what happened to Elsie. We also know for certain now that William has been trying for 30 years to cheat death. Finally, we know for certain that he soured on it and considers it his "greatest mistake." It seems even more likely now that he's heading there to destroy what's left of it, lest someone, say, gets the idea to clone his awful self like he tried to clone his awful father in law.
The big, new question that we got is who Ford made Bernard create a second control unit for. It seems to me that there are only two people important enough to Ford to do that for (and that would provide the greatest twist for the show): Ford, himself, and Arnold. Might Ford have cloned
himself and might that clone have been who Dolores killed? That would open up the possibility of Hopkins returning this season or next.
If that's too much of a stretch, then Ford might've intended to bring back Arnold as more than just a host and as close to human as possible. It'd be pretty trippy if Bernard were commanded to create a control unit essentially for a new version of himself. It's a bit unclear to me if you can create one of these new clones from an already-dead person or whether you need an imprint from a living person, though. If it's the latter, that would rule out Arnold, but Bernard is so like Arnold already that it makes you imagine that that wouldn't be a requirement.
Well you guys guessed right with the daughter thing.
FWIW, you were right about not putting too much stock into imdb.com credits. Young William, Elsie and Stubbs have all been in more episodes than they were originally listed as being in and the woman listed as "Grace" is William's daughter, Emily.