No worries on the skill level. We all start somewhere and it's to be expected. As long as the desire is there to learn more, it seldom becomes a hindrance. These forums exist for the sole purpose of helping people develop their skills, so never feel like you can't ask a question.
Now, onto your part. Right off the bat, I want to make sure you know your 2D contour in the "Front Inside Panel Cutout" is cutting on the inside of the part. I suspect you want it on the outside. Go into the Geometry tab. You will have to zoom in, because the arrow you need to toggle is very close to the triad and zoomed out is almost impossible to see. So, zoom in to where you WCS is and you will see a separate red arrow. Clicking on it will tell the operation you are looking to cut on the outside.
As for the 3D pocket issue. I honestly have no idea. I've played with every setting I could think of. Maybe it's this. nope. Maybe it's that. nope. Even if I set all my stepdown parameters to full flute length, it still kicks out the same 4 depths of cut.
Maybe I'm the odd one out, but usually when I encounter an issue, I'll give it a few moments of trouble shooting and then quickly abandon that approach in favor of something else that I know will work. In this case, I know 2D Pocket will get me exactly what I want with no issues. Side note; You can also use Horizontal (in the 3D tab) with decent results. However, you will need to use the patch tool to cover the speaker mounting holes. The toolpath will just be going around the holes wasting time and likely not removing what is needed
So, 2D Pocket. Select the inner and outer diameters of the speaker holes and just the outer diameter of the 23mm holes

Heights; set to "Selected Contour"
Turn on "Multiple Depths", set Max Stepdown to 5mm and "Use Even Stepdowns"
Seth Madore
Owner, Liberty Machine, Inc.
Good. Fast. Cheap. Pick two.