You could replace the sticks with Magsticks (which are 4/8 way switchable) or U360s.
I've got my buttons in a cluster arced like yours, but I have 2 rows, 4 on the bottom, 3 on top. They work perfectly fine for me.
As for the middle of the panel, I'd consider putting a trackball in, though I can't tell if there's enough space for that.