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Hi, Welcome,
I am also relatively new, a little over a year ago.
More than suggesting specific modules, I am going to give you some opinions and suggestions.
-Case point. It's a shame you already have the case, 3U 84HP is a very limited space. Surely in a short time you will have to choose to expand. I wanted to start with 3U 104HP, in the end I started with 6U 104HP and a few months ago I added 3U 104hp more. They are not full at all, maybe 70%.
-Brains point. I am not a fan of brand B but what I can tell you is to avoid "reduced" modules. If you go for MI clones, you better try to buy them in the original size.
-Next module point. I am not sure which clock you are going to use to trigger both the VCO and the sequencer...
In your case, and to have as many functions as possible, I would recommend Pamela's NEW Workout.
https://www.modulargrid.net/e/alm-busy-circuits-alm017-pamela-s-new-workout
A single module that offers you clock and modulation functions. In the second-hand market you can find this version at a very good price.
For me this would be the next module, with a Veils type VCA.
The clones are at a good price.
For example https://www.modulargrid.net/e/tlm-audio-vacs-veils-2-clone
Now to continue you will surely need function generators (Maths, Rampage or similar), effects (important for generative and ambient), matrix mixer, LFO's (Batumi,...), and surely incorporate another voice, perhaps an MI Rings (a classic), or a complex VCO.
Money money money...