I'm new to freecad, so far I made it this way :

Sketch a rectangle for the top surface, pad it, add filets for the corners. Then select to bottom face, make a new sketch, another rectangle, then a datum plane 40mm below, sketch another smaller rectangle, and make a loft between the two to create the bottom of the tray.

Now for the hole I made a rectangle on the top face and made a pocket with an angle.

Downside of this, the thickness of the walls is not equal. Ideally I'd like a 1.5mm thickness everywhere. And I'm not really sure how to proceed to make the separators inside the tray.

What is the most efficient way to do it? thanks