Careful...the 531 mixer doesn't have CV over levels, but over panning.
This build can't properly support huge modules, either. You need to sort out how to get the modules down in size so that you can make something usable here. One example would be the use of the SND/RTNs...you can get the same basic functionality out of a Ladik A-520 and P-520, with the sole difference being that you'd have to control your I/O levels on the stompboxes themselves. But as for the space difference...that would half that, and the COST...$78 sounds WAAAAAAY better than $500!
One other thing: you'll probably find that you'll hate having your control surfaces on the top row. In that position, you'll have patchcables all over them and they'll be a PITA to work. Bring them to the bottom row, then all you have in the way will be the 2s to/from patches.