Thanks for your detailed response - very helpful!
I agree it makes sense to go for a bigger case and so am now looking at the Doepfer A-100P9 Case PSU3 with 3x 84HP which also has a handle and cover I think which is great - I have updated the build with this in mind.
I took your suggestion for the Intelligel I/O (just what I was looking for - perfect!).
I wasn't quite sure about what to go for in a 2nd filter but the Bastl Cinnamon seemed pretty cool sounding and good value for the size.
I added in an additional Doepfer ADSR.
I know what you mean about the Plasma Drive but its so damn cool - I may in the future move it to its own individual case to use as a distortion for some of my external gear.
For the Oscilloscope - I am a visual person so would like to see what it is happening with the sound that is being created - is there something similar you would recommend that maybe takes up less HP or is a bit more basic? I guess I dont need to monitor 4 inputs at once but maybe 2 waves may be helpful.
One thing I am now not to sure about is I was thinking of using a Beatstep Pro to act as a sequencer and sometimes to sync between my computer and the system - not quite sure how this would connect in this build though?
Also with regards to layout, I am not quite sure what works well - I guess that is the point though of moving things about once you are using the system for optimum efficiency.