I'm starting to plan a corner kitchen cupboard to go next to a regular cupboard that already exists. I have made a model out of cardboard. I have a few questions I hope you can help me with.

1) How many millimetres should I leave either side of the door? (I realise that that would make the edge that the door sits on longer, thus making the left-hand edge of 532mm longer).

2) How should I deal with the doors overlapping?

3) Should I have a return on the right-hand 230mm edge?

Corner cupboards are advised to be attached with space on either side due to never perfectly square walls as well as doors running into each other. Narrow lengths are then added as filler. You could build two stiles onto the case, build the door slightly smaller than flush, and then trim it down to what not only clears the door next to it but also looks good aesthetically, given that there will have to be some stile showing on the left.