A few questions from the "new" player

[Halivel]

I started the main scenario from the very beginning with my friend. We needed to kill 5 mobs. But in this location, the invisible WHM (it seems like level 80), killed these mobs with one hit. He wrote in a general chat something like "go away little idiots. Go to school." These mobs spawn for a long time. And we just do not have time to run to just appeared. How is this possible?

This person was cheating most likely, which is reportable and bannable. Also the fact they insulted you for the fact you are a new player is a harassment, which is reportable too. Basically, they broke at least 2 lines of ToS just in 5 minutes.

Another case. We stood at the entrance to the dungeon. A player with a nickname something like “dgsg dfdsfs» runs up to the NPC, stands next to him, moves away and disappears near the steps. Again, out of nowhere, the same player appears, dressed exactly like the previous one, but with different letters in the nickname, speaks to the NPC and dissolves in the air. And we have counted 14 such players. How can this be? Where do they disappear?

These guys were bots, and their holders also cheat to do things faster.

In the initial location of Thanalan, I saw a player who ran on a dais through the air. I did not find such a thing that would give me this ability. Completing quests would be much faster with this.

And this was a cheating as well. I would notice, though, that in locations starting from HW up to ShB you can fly, but your Bard is 67 level I believe you already developed this. 2.0 Locations (those before Heavensward) aren't available for flying without 3rd party tools.

Only on the third day I finally got my house in Kugane. But I don’t like its location as much as in the second house.
I watched a video about buying a house. And turning on the movies in the little window, I sat for days, clicking on the sign. I sat and constantly clicked.. to the pain in my hand. I really wanted to buy this house, it was located by the sea.. a beautiful landscape.
I did not pay attention to battle classes, I like to craft. Collect something, etc. And I was glad to collect the required amount and finally buy the beautiful house with this money.
I stood by that house alone. And clicked on the poster. And then .. the player runs on the mount and immediately buys it. Is that such luck? Or the timer shows when this house can be bought? So I sat constantly clicking on the sign and it was all in vain? I do not understand..

As the system works now, you don't need to wait for the timer you're relocating the house, which is what that player did, apparently. It's not a pleasant feeling to see how the house you want just goes away in front your eyes, but it's sadly often the same irl. XD At the other hand, with relocating that player freed another plot. Maybe that one you got yourself later. Also, since you have a house now, you can try your luck and get the plot you really want with relocating when they will add new wards, which will happen with 5.1. release.