1. That was a REALLY well crafted movie. Felt like everyone got a fair and complete part, which can't be easy with ~20 heroes, half a dozen villains, 6-8 mcguffins, and a plot. A logistical miracle with no wasted motion. And after all that... there's still a lot of meat on the bone for ongoing storylines. Contrasts very favorably with something like The Last Jedi that tried to do essentially the same thing with fewer moving parts but fell short (imo, obviously).
2. Everyone who got dusted is coming back. I thought this was pretty obvious from Dr. Strange's comment, but i was still able to enjoy and get into the emotion of the dusting. I don't follow movie news enough to know who has sequels, it just seems logical. I don't think they'll use time travel or an alternate universe, the gauntlet will be able to undo it's own works.
3. Of those with real deaths, they could feasibly bring back any of them. I hope they don't. The best though would be Thanos resurrecting Gamora and that being the action that leads to the undoing.
4. Really funny, and most of the jokes landed. I enjoyed Ragnarok, but thought quite a few lines fell a little flat because the humor was repetitive and predictable. The only line that kind of made me roll my eyes was "that's what getting killed means". It was well delivered, but it's a variation on a joke that has already been used a number of times. Other than that, this movie was still fresh while staying true to the characters.
5. It's interesting that Stark, Thor, and Cap are probably the most willing to sacrifice themselves but they were all left alive. I think one of them gets it destroying the gauntlet. Argument for Thor: his world is already gone, and at some point it is going to get (more) obvious that he's 1500 years old but aging rapidly. That says, i think it'll be Cap, Stark will get to ride off into the sunset and live happily ever after.