3) Do you think that Asimov was ultimately successful in melding together his two universes?
Three universes, really: the robot series; the Galactic Empire series of The Stars, Like Dust, The Currents of Space
, and Pebble in the Sky
; and the Foundation series. The latter two weren't originally connected despite both involving a Galactic Empire. Plus he managed to indirectly tie into The End of Eternity
as well, though the latter is a more inexact fit.
From what I recall, I think he managed to fit them together moderately well; it helped that most of his fiction built on certain common assumptions and technological tropes, so there were some built-in similarities even without explicit connection. But I did feel it got a bit overindulgent, and some of the later novels felt more like extended exercises in continuity-stitching than anything else.
But it's been a long time since I read them, and there's one, Forward the Foundation
, that I've had for years but never gotten around to reading. I've been meaning for years to get a complete collection of the whole continuity (just the Asimov books, not the ones by other authors) and read the whole thing through in more-or-less chronological order, and I recently managed to complete the set, but I've been too busy with other stuff to get around to it yet.