The Roland 531 offers six channels of mixing plus pans and pan automation (CV) on every channel. You may or may not want to ditch it depending on your anticipated needs.
The Disting mk4 can only be dialed into one set-up at a time. So you can't use it as a filter and a distortion effect at once. You have a little space left in the rack as-is. I think there's enough room for a 2HP filter.
If you're coming from Ableton you may want to consider a 1010 Music Toolbox as your sequencer rather than the Metropolis. It takes up less space and the workflow is similar to a DAW rather than a classic modular sequencer. That will give you more space for other modules. The springray is just an interface for a spring reverb tank. So you'll have to haul it around with your rack. If that's not a problem, cool. If it is, you can probably replace the SpringRay with something DSP based that is smaller.
The cost between a passive 1U mult and an active one isn't enough to go with the passive. I'd go active and not worry about it. (respectfully disagreeing with Lugia).
That Atlantis module is the real pig in HP real estate, I'd sacrifice first (personal opinion). It's a self-contained synth voice (oscillator, filter, VCA, etc.). So you may be better off using the space for a dedicated filter, another dedicated oscillator, and perhaps some other modulation/envelopes.
Xaoc is coming out with a new envelope generator (digita), with four envelopes. I'd check that out as well and see if it fits into what you're after.
I just started a second 104HP 7U case and most of the space is already accounted for. So you'll really want to consider the size of the modules you've selected, their value, and any need to expand. No matter what you do... you'll feel like you're "wrong" about your choices and then rethink your plans about 4-5 times. Best bet is to build in stages rather than all-in so you can rethink your plans once you've got some knob wiggling time under your belt.