After some testing...

The cupboards and storage areas are basically built as a frame. The faces of the units were initially built using cheap chipboard. This was used to work out where doors could/should be, allowing for the sink/burner positions etc. Then the doors were rough cut out of the chipboard to make sure they could be opened when sitting in the main seating areas etc.

Once the “final” design was complete, the rough panels were sent off to a professional cabinet maker who then transformed the rough prototype into the finished article.
The main cupboard is made from MDF with a real European oak veneer which was then lacquered. The handles were chosen to be ok to lean against when the wan was in bed mode. The doors are kept closed by magnet latches.

Other units were made from chipboard or ply and then coated with the grey lining material used on the walls.