Hey there,
I just thought about a new levelup reward system... and I wondered if I could calculate basic Stats like HP, Mana, Damage, etc as follows:
Basic Value + x*PlayerLevel

Well, as far as I know it works this way right now.
HP=160+40*PlayerLevel
You can change this in the graphs.

Could this be implemented to roll Dungeon/moster/Item levels? lets say I enter a dungeon with level 6 and monsters automatically roll between 5 and 8. Meanwhile I level up and now monsters spanw between 6 and 9? same for Item drops...

You can achieve this - kind of. But there is no perfect way since the player can always return to a dungeon of a low level when he reaches a high level, and monster/item levels are set when the player enters the dungeon.

Using your example, in the dungeon editor you would set Player Level Match Range to 6 and 9. If you then also set Match Offset (next box along) to 1 or 2, that would allow the dungeon to scale up one or two levels above the player. So if a level 8 player entered the dungeon at level 6 it would scale up to 9. If the player is level 10 and the dungeon level range is [8 - 12], an offset of 1 will make the dungeon level 11 instead of 10.