re: hidden hinge

Given that thickness, the 5mm is really the only choice. The Soss pictured above is too large (the smallest they make is 10mm and requires at least 10mm depth).

The other option might be a quadrant hinge: http://www.woodcraft.com/Product/2003454/2674/Economical-Quadrant-Hinge.aspx

You’ll have to mount it to the lip of the rabbet, which will be tricky given thin stock.