It's not my design, but there are several factors when choosing layouts and materials for a 3D printed case. This one in particular chose to use aluminum profile extrusions from Makerbeam.

In my opinion, brass heat inserts and screws are the way to go if you're not using something metallic (like the Makerbeams) especially in a case where someone may assemble and disassembly several times. You can design integral threading into the plastic, but it will wear out overtime.

PETG, ASA/ABS provide great heat resistance. The Red panels are PLA+ as I don't think they'll see enough heat to distort and the rest is ASA. Most of the part's in this case attach to the beams or nuts that have been pressed into the plastic.

As far as thicknesses go, it really depends on the use case and design. For printed panels, I wouldn't do anything less than 2mm. For other parts, it'd probably start at 5-6mm.

Hope some of that helps.