With the 3D part in my hand, one of my questions has been answered. The height of the relay is just a smidgen shorter than the uppermost ledge which is about roughly 5mm. These ledges are responsible for the Lower Interface panel not dropping into the whole cavity. The 5mm height limit is quite a lot of space for the electronics since all the components are SMDs.
On the relay’s spec sheet, the component has a height of 5.2mm with the legs in ‘normal’ position. Once I squashed them, it was slightly shorter. However, I have to take into consideration that when I solder the leads from under the PCB, the solder bumps might raise it back again.
Eventually, when the design is ready, I will want the board’s thickness to be 1.6mm, leaving me with about 3.4mm to play with. 2.0mm thickness is great but I just realised, this will affect another component. The board’s thickness would raise the LEDs closer to the panel and reduce unwanted light spread. As for the four function lights (ALPHA, BETA, GAMMA & DELTA) I might have to scratch-build some kind of light blocking piece to address this issue.
