Cool! I would still recommend getting rid of the Doepfer A-138p performance mixer. There are more important modules to start with and if you plan a rather small rack at first (which is absolutely the right way to go!) it is oversized. Plus, your maths and the intellijel vca can mix signals.
So I'd very much advise to get a proper VCO in its place. That is something you really need.
Also a nice filter is a good choice. You had one in there before, right? Doepfer has some good ones, but there is really a ton out there. Same infinity of choices as with VCOs...
And you might check out the disting: It is a slim module with lots of functions; might be helpful if you don't have much rackspace.
Also, try to figure out which modules suit the music you want to make. If you want to play melodies you might consider getting a sequencer. If you want to do droney/ambient stuff that might not be soo important (although still good!).
Most probably you won't need an audio out. If for example you want to record stuff on your computer you can probably go directly from a vca (or whatever) into the interface. Normally interfaces can handle the hot (loud) output of a modular. (But it's best to check that out before hand.)
Generally speaking it is good to start with a few modules and get to know them really well before expanding your system.
It is also the best way to not get frustrated by an overkill of possibilities at the start.
Good luck and... have fun!