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Hmmm... To keep it close to your budget, you will probably want to stick with clones of the Mutable Instruments modules. They are smaller, cheaper, and sonically identical. The only real downside is the ergonomics because of the diminished size. I would recommend a Marbles clone (Cara) for your random gates/sequencing interests. I believe it quantizes. I always recommend the Malekko Varigate 4+ sequencer for small builds as well: 4 CV or 4 gate or 2 CV/2 gate sequencing with quantization.
In regards to the video you shared and the Boards of Canada interest, you may want to consider the ZVex Instant LoFi Junky and a small multi-effects unit for the warbly, wobbly vibe. You could substitute a Rings clone instead of the Elements clone (Atom). I would consider adding some sample playback capability too (Disting Mk 4 and Radio Music) for the BOC feel.
I put together a quick rack based on your ideas with a Toppobrillo Stereo Mix 2 instead of the PanMix, though the PanMix looks cool. All of this would fit in a TipTop Mantis, supplementing what you already have, and still leave you a little room to grow.
Have fun and good luck!