The problem I see here is that players will definitely become confused as to how they are going to choose the spell level. The spell slot icons on the action bar have to have very strong cues to attract user's attention, because at this moment users look at a different part of the screen. This would be a UX disaster!
This isn't difficult in the slightest. You click on a spell, the relevant slots in the action bar highlight/glow/enlarge and you 'choose your casting level'. It's suddenly very clear for new users what these slots relate to, you can animate them being expended. It's super easy for experienced users to evaluate which casting level is best given the available slots. Particularly when we have 6 banks of slots at 11th level.
Right now it's an absolute mess with so many repeated icons with numerals on them. Changing them to arabic isn't going to help, it's still unclear whether the number is spell level, key shortcut or even remaining uses.
