There is some nonsense going around about his wages being 330k but the more reliable reports - as well as common sense if you know the club, its wage structure, etc - are that he is on around 200k base going up to maybe 230-250k if bonuses are achieved. That puts him in the same bracket as Jesus, Partey, Rice and probably where Odegaard will end up as well.
In terms of his role, I think you have it right with the caveat that I expect the biggest change from Arsenal this year to be less reliance on a set first XI, with more rotation and lineup switching based on matchups.
Havertz seems likely to get most of his time as the top left of the four man midfield box when in possession in that 3-2-2-3 shape, then to be one of the advanced central pressing players (along with the CF) in a 4-4-2 shape out of possession.
But I think Arsenal will also have matches where we play Rice in that role and Partey as the 6. And while Zinchenko will sometimes be the LB who inverts into center midfield and plays as the bottom left of the midfield box, we'll also have a lot of games where its either Kiwior doing that or Timber doing it from the right side.
Overall, Havertz provides a much more potent attacking option than Xhaka in that role and I think the idea is to then strengthen defensively behind him by (a) having Rice the most common 6, rather than Partey and (b) having Zinchenko become more of a rotational player for certain matches, rather than an automatic starter. So overall the front five become more attack minded and the back five become more defensively sturdy but there are many different configurations possible based on the opponent and the game state.