I like the layout for the space. Getting so much on a small control panel is hard.
Make a quick one with cardboard and try it out. It really helps. Or make one with some scrap plywood! Then test.
But I vote for a few more buttons for the 4 way or none (and maybe move it down a little) to make use of the buttons for the 8ways.
Also, I like my buttons for the 8ways straight across. But that was how my local arcade did their SF games when I grew up... It's all about what your used to....
If it's for an arcade machine, consider hotswappable control panels, and make 3. One for 2 player 8ways. One classic arcade with a 4 way and what I did was the buttons for asteroids next to it (and qbert after that)... Great classic CP. Then a trackball one. For the trackball one (and spinner one) it also is great if you can find an 8way flight stick / Tron type stick. Adds a TON of games that can be played there.
If its NOT an arcade machine (standalone CP)... Make 3...
Breaking up CP's and making each work better by themself In my opinion is MUCH better. Allows you to do SO much more! And add later!
Good luck