My modular consists of just a Mother 32, a second VCO, and some utility modules at the moment, but it is growing. Take my opinion as one of a beginner, but I've had the M32 for a bit now.
I agree with everyone above that for what you get function wise, the Mother 32 is compact and very affordable so its a great jumping off point. You could barely afford a good Moog type filter and VCO for what the M32 costs, let alone the other modules you would need to get rolling. I've had a couple of frustrations though: For lead sounds, the AD envelope with sustain switch is pretty limited for shaping (and since you have a Sub37 I assume that might be important). Adding an envelope means adding another VCA since you can't truly bypass the M32's envelope's affect on the internal VCA. Also, want to add another VCO and hard sync? Well, you can add VCO's easily, but you can't sync them with the M32 which would be nice for tighter bass sounds.
These are nitpicky things, and I really love the sound of the M32's VCO and filter, and being able to rack it with other gear is nice..... but makes me wonder if the Moog Grandmother might be a better intro into modular these days since it is a definitely more "complete" of a monosynth already before you start interacting other gear with it.