There’s two types of things a computer does: calculations and moving around data. Within Krita, the latter is most common. Thus the most important thing is lots of fast ram.
The pixelbrush is multithreaded, as are many filters and parts of animation, and wherever else we can stick in threads and get performance gain. So a lot of cores is useful as well.
Graphics card isn’t that important for Krita, more useful for Blender and Godot(and even there, anything reasonably recent can give plenty of speed).