Firstly, my workflow isn't the only workflow. This can be created many ways. I just wanted to show some techniques that can be helpful. I uses the offset faces after the shell command to avoid having to use the offset tool in the first sketch.
My personal preference is to use 3D modeling features instead of sketches. It makes sketches simpler and more reliable. I spent much less time sketching and debugging sketches. While it is counterintuitive, it also creates computationally faster models.
The purpose of Sketch 2 is to create the outline for the openings in the sides. I created it on an origin plane rather than a face of the existing 3D geometry. Origin planes don't change and as such are a more stable reference then faces of 3D geometry.
I project/Intersected the body into the sketch. A body is a more stable reference than individual faces:
then I used constraints to make sure that the little rectangle for the cutout is always centered horizontally in the tab.
Sketch2 and Sketch4 are independent and have nothing to do with each other.
The way I created the holes is one way. I could also have only created and dimensioned one point, created one hole on that point and then rectangular patterned that hole. The nice thing with the sketch is that you can see the distances between the holes in one view without having to edit another feature.
Chamfers and fillets do not belong in sketches if the same effect can be achieved using 3D modeling features.
Again, keeps sketches simple etc.
Decorative chamfers and fillets are secondary or even tertiary features and should be applied as late in the timeline as possible. You never know ahead of time when you want to reference an edge of your model for example in another sketch for another feature. It helps if that edge doesn't have a fillet š
Generally mirroring and patterning (both should also be kept out of sketches) are powerful features, that when used wisely can significantly reduce the amount of modeling.