Don't have the full game, but have seen a decent bit of gameplay and done some digging in the forums while considering whether to buy the game myself. Can't answer all your questions, can't be totally confident of all these answers, but I hope these help:
dlder: o) can the view / view distance be changed? One only sees as far about 4m
As far as I can tell, no. The limited visibility (other than the direction the camera is looking in) seems to be a deliberate choice to force decisions on where your attention is focused.
dlder: o) can a button be bound so that you can rotate the view with the mouse? Like while holding "r" you rotate the view, not the character?
From what I've seen of gameplay in the full version, it defaults to using mouse movement for view control. No need for a button to do it.
dlder: o) can the buttons be remapped?
The devs confirmed before release that there would be remapping in the full game. I haven't seen how it's implemented, how good it is, or if it supports gamepad remapping or only mouse and keyboard controls.
dlder: o) is there any way to fight methodically? Because you see the enemy about the same time when he sees you, he'll rush you and you have to fight him with your sword. And then it's just clicking the mouse button until he is dead. Or you are.
Combat feels... slow and boring and without any merit.
Firstly, it's a stealth game so the goal should generally be to not get into fights. I personally tend to like figthing in stealth games where it's an option though, so it's been a topic I'm curious about too. With that in mind, what I know of the game is that there's a parry mechanic and a charge attack mechanic which both allow you to essentially turn any opening you can create into a multi-hit combo attack. As far as I can tell, those mechanics were in the demo (I haven't had a chance to play it myself) though. Not sure how much you've experimented with the mechanics, and what I've seen makes it look like the charged atttacks are pretty hard to actually pull off, but there's more than just "mash attack button" as an option when it comes to fighting.