My panel has its roots in a 3rd party kit that was available from Affordable Panels so I have some experience with the modular panel concept. The good news is if you want to change part of the panel it is easier to do. The bad news is there are more pieces to fit together so it's more difficult to get it all to fit well. In the Affordable Panels arrangement there is a sub-panel behind the panel sections that you see. The visible panel sections are then screwed to that sub-panel. I do still like the idea, but I'm sure it is more work than using just a single panel piece.
I started with the Van's supplied DXF drawing and sliced it up to fit the Affordable Panels layout. You could slice it however you want, but I tried match the sub-panel that I had. Once I had those sections I was able to move on to the next step.
I created my panel sections using the Front Panel Express tool. For their tool you need the outer shape of the pieces which came from the DXF file. I like the FPE services but it can tend to be a little pricey and it tends like all things to be getting more expensive. However, it has allowed me to build a visually professional looking panel which is powder coated and engraved.