Here are all the walls I have made so far, plus I found a Necromunda doorway which seemed to fit nicely so I repainted it and added it in. I have made 6" lengths, 3" lengths and the doors which are 3" too. I may make some right angle pieces, but not sure. I like the fact that these can all be packed away very easily, building lots of corners or T junctions could spoil that.
The next stage has begun, last night I cut enough foam board to create 16 more 6" lengths and 20 more 3" lengths. That should be enough. It gives me 24 of each.