My rule of thumb for small to mid-sized builds is:
-- 30% or less HP is voicing (OSCs, filters, waveshapers, etc.)
-- about 30% is CV (sequencers, envelopes, LFOS)
-- about 30% is utility (VCAs, attenuverters, etc)
-- 10% other (finishing FX, etc)
... I find this reliably gets me a usable mid-sized build. For larger builds, once you have your CV/utilities core, then you can take a freer hand with what else is in/out and still get a usable setup
So a few points of feedback on your "get started" rack above
-- it looks heavy on voicing and light on CV, I think you'll miss having some CV sequencing, and could use more CV envelopes / LFOs. Consider MI Stages, Intellijel Quadrax + Expander, Instro Ochd. Those would help give you more useful CV.
-- its also light on utilities, kind of bare minimum above. Consider things like MI Links and 4MS SISM or Tiptop MISO, though Maths gives you some of that type function. Also, Maths is great, but I'm not sure it makes sense above given how little other CV there is in the system
-- you do have IN and OUT modules, which is good. But these are worth some real homework, e.g. maybe something like ES-8 will be a better longterm fit round trip to the DAW for you? And the OUT merits more attention, depends on what your needs are. Lots of OUT options on the market, I use 4MS ones because they have good headphone and mains outs. This is not to say the options you have are bad, but to highlight that there's a lot of variety available in the marketplace and better to get IN/OUT modules that are a particularly great fit for your setup and uses.
-- regarding sounds sources, there are tons of options in the market. If you're not set on one, I'd say shop around more and consider what will be inspiring for you.
Regarding learning modular, there's lots and lots and lots to learn. My best practical suggestion is review a ton of Lugia's draft racks and posts describing draft racks. That will give a lot of insights on "what and why" for particular design goals.
Hope this helps. Good luck, enjoy!