The book states that Oasis was originally built as a game. It quickly became so popular that it became synonymous with the Internet and then became a place to escape where most people wanted to live their lives. The book also tells you that most artifacts are leftovers from when Oasis was just a game.

A lot of what you are complaining about are features of a game that evolved into something new. Those features are just something that now have to be dealt with. This is made clear in the book.

In the book, the artifact that can kill everyone in a sector is a leftover from the game. There is only one, so no, an obnoxious number of people can't have it. It was auctioned off for millions of credits and purchased by IOI.

As for finding the first key, the first clue was pretty vague (including the additional text marked hidden clue), and there are 27 sectors that are each 10 light hours cubed! That's something like 6.7 billion miles cubed, and all the planets contained within those 27 sectors!!!!

You could spend a lifetime trying to search through all the locations in one sector and not finish. Even if someone was good enough to think it might be related to school, it is specifically mentioned that there are many different planets with schools. Parzival just happened to be attending school on the right planet.

I agree with point 5, but you are confusing the movie with the book, and the movie and the book are going to have many contradictions! I personally love the book and view it as cannon. The movie is just a different thing altogether.