SPOILER ALERT! Questions After the Movie

Rating: 9/10 (26 April 2019)

SPOILERS SPOILERS
I loved the movie! There were some awesome moments in the movie that were beyond words. I will not talk about those moments, per se except to ask questions, but I have a few questions that I have for things that don't add up. These are addressed here:
No one really knows the rules of time travel in real life, but there has to be things that I believe would be obvious.
1) How can future Nebula shoot herself from the past and still be alive.
2) Wouldn't doing what the Avengers planned and completed made what Thanos did in Infinity War obsolete? Since Thanos was killed before he completed his Infinity War mission, would that not make many of the Marvel Movies irrelevant? It would make Infinity War irrelevant for sure.
3) When Spider-Man returns to school he sees his friend. In the new movie it appears the core group is still together. Maybe the movie will explain it, but that what indicate every one of Parker's friends were directly affected by Thanos' snap.
4) How could Captain America going back in time and staying there not affect the future and how it transpired? Rogers would have to be a total Social Recluse and never go outside.
5) Since Gamora comes back due to the sacrifice of someone else, wouldn't that mean that people like Ludlow and Alexander Pierce are now still alive? Is Gamora still alive? You see Quill looking at a picture of her, but not her.
6) THIS IS NOT A QUESTION BUT MY BIGGEST NEGATIVE IN AN OTHERWISE GREAT MOVIE- I did not like the fact they bringing everyone lost back 5 years later, I get Stark's point of view on this, but this would be disastrous for the 3.5 Billion coming back to life to a world in shambles. I also wish the Time/ Space aspect was more seamless. It seems like they took some liberties on how it could logically work.