I’ll do my best to answer your questions:
The weekly PVP event resets at the same time for everyone, but if you are playing when the reset happens, it won’t take effect until you log out and log back in. Once a player logs in, their rank is reset back to 15. If you log in right after the reset, you’ll get a mixture of players who have reset and some who haven’t.
The matchmaking is always over a pretty big range. I’m level 440 or so and will see players as low as 200 and as high as 1000. I have had players as low as level 4 invade me within the last few weeks. Another factor with the matchmaking is your PVP rank. When you start a new event at rank 15, you will get easier matchups. Once you climb up into the last few ranks, you will get more difficult matchups. But there is always some random variation and you can see a pretty wide range of players at any point.