Since you have the space, maybe consider a Doepfer A-143-9 instead of the A-145-4...
I would agree with everyone that you shouldn't necessarily plan everything out. I have a Rackbrute 6U filled out and now a 3U. I think in time I will get another 6U to combine with my existing 6U...I like what I'm building with the 3U accompanying my Minibrute2 keyboard synth...lots of effects/modulation in my 3U that really compliment/extend the Minibrute2.
JB