Pathfinder approach is probably best.
Conceptually yes, though I have my misgiving regarding how small buttons for extending menus are and how easy it is to misclick when switching between spell levels. I had to reload in Kingmaker multiple times, when I made a move order what I wanted to hide the tab - especially problem in turn based mode, where the character will just walk, eat bunch of opportunity attacks and waste this and the next turn that way. But overal, it's solid.
While we complain about hotbar - I really hate the abilities which when used spawn another ability - so like recasting Ranger's Mark or Witch Bolt. It's adds to hotbar chaos, even after thorough organization.