Thanks for the feedback and info, I found where to manage the materials, and I updated the model trying to align the buttons, I did my best but I'm very amateur with blender yet...
Since the idea is using raspberry as the main board and there are already cases and faceplates for it, I took measures for the faceplate from a faceplate from adafruit (adafruit.com/products/2807). To decide measurement for the body I need to know the size of the numeric matrix keypad, other keys and connectors.
Regarding the d-pad, you are right, I don't like the d-pad either, I've been searching for radial buttons to get inspired and I found a few ideas from games and interfaces:
So I'm sure I will change that ugly d-pad.
Yes puting the phone over a table or near to a proportionate object will help to see proportions, but first I need to rebuild the main parts of the case with a cad software, I've been thinking to use openscad to create a case model with perfect proportions and then export it to blender to keep working on it.