Before the story progresses in anyway, just letting you know, some people asked me questions in PMs.
Mega Evolution is a future mechanic, Kalos and Hoenn are the main regions this is naturally obtainable.
Z-moves are an arguable. There has to be a real reason, like it being found or obtained and it depends on who has it.
Dynamax and Gigantamax will only be mentioned, it is a byproduct of Eternatus in Galar, and will only be accessible in Galar.
You are allowed to have an Egg in place of a Pokémon.
you can have armor, but not weapons. However, it's possible for a weapon at the last second from a Pokémon like Honedge, but it's a hundred percent circumstantial, you can't have a Pokémon just because of that.