Thanks for the detailed answers.
I have completly forgotten that one Nebula killed the other Nebula. I was worried that she deleted "herself" from the timeline. I also couldn't remember to see Gamora on the GotG's ship. Maybe that caused the confusion.
I was also not a big fan of depressed Earth. I know 50% of the population is a huge number, but we have to believe in humanity. Even if such a rate of people would die, the survivors would live their life. So I couldn't imagine such things as empty harbours or stadiums in New York. Life finds a way as we know it from Jurassic Park.
I know this is "only" a comic movie, but Thanos' plan was wrong from the beginning. Even if he could have killed half of the universe, the other half will still procreate and have next generations. So the whole snap was meaningless in philosophical way as he must have used again and again if he wants true balance. Then they have changed his motivations for this movie, so he really turned into an evil character.