Is there a way to rotate the brushes and predefined tips? GIMP has a very handy rotate slider alongside the size and opacity sliders, and I was wondering if it's possible to set something similar up in Krita.

Press F5 to open Brush Editor.
Click on "Brush Tip'
Change the value of Rotation or Angle depending on the type of Brush Tip you are using.

You can learn a lot there: https://docs.krita.org/Category:User_Manual

Thank you, artur.