If you're going with Intellijel 7U, get the 104 case. You will eat up module space much faster than you think. Also, be aware that the power supply eats up a lot of room in the lower 3U row. You won't be able to put modules that are very deep in that row.
You might think about replacing the Intellijel MIDI interface with an Expert Sleepers FH2. The built in USB/MIDI connectors on the back of the case are nice. But the FH2 will offer you a better interface with Ableton Live. Plus you can edit your set-up via ES's web interface (optional) and expand the FH2 for even more CVs and gates. Plus the FH2 can do LFOs, arps, and envelopes. They aren't as easy to set-up as a dedicated LFO, ADSR, but they are useful.
In your initial set-up, you'll probably want to add at least one filter, a set of VCAs, and at least one LFO... unless you're going to rely on the Mother-32 for that.
It may be a little early to add the Metropolis until you get some wiggle time in. You can always sequence via MIDI through Ableton to begin with. Maybe a Pittsburgh Micro Sequencer to start with?