As far as mixers go, it kind of depends, while the WMD performance mixer is great you could get away with something like the cosmotronic cosmix, you definitely can get more value with an external mixer and save the HP.
I agree this is a bit weak on VCA's.
I find sequencers are a very personal item and really depends on the workflow you are looking for. I have several and each has a purpose, one I don't think is mentioned a ton but is my favorite so far is the NerdSeq, as far as step based sequencing I don't think there is a more powerful sequencer 10 tracks (6 modular and 4 sample/audio including fm voices). While I wouldn't consider the sample tracks a comparison to a dedicated sampler (limited memory) they are a nice to have for some added spice, or you can use these as basic oscillators including 2 or 4 operator fm.
I try not to emulate the gear choices of artists as this rarely works out, what workflow works for one artist won't likely work for another. I remember when I was young I brought my drum kit to a party and another drummer used my kit and pretty much showed me I had a lot to learn because I never heard my kit sound so good, I never was able to reproduce his "tone" on my kit. Same kit different artist, completely different result. Its your instrument to develop your workflow and your sound.
If you really want polyphony you are better off getting a polyphonic synth, it can get really expensive really fast in euro and still be a struggle to dial in a sound as quickly as a good poly synth will. State Azure is a good example of a mixed mode artist that incorporates lots of different gear and is not strictly modular and that gives a lot of flexibility and can save a ton in costs.
As others have mentioned, start small. Sound source (plaits is great because it is so versatile with built in lpg/vca), a way to sequence and a modulator, Maths is a great choice. Start here the perhaps add some fx, Beads or an FX Aid, and away you go.
Pip Slope, I think there are better options Maths has great envelopes. I think Acid Rain Maestro is a great clocked modulation source when you start reaching for more modulation, and if you want more function generation/envelopes you can always add a make noise function or a joranalogue contour 1.
I have several Instruo modules they are great, but on the expensive side. I think there are better options here as well. The Dixie II+ is a great analog voice.
As far as samplers go, I think the Assimil8or is the best eurorack sampler hands down, it is a bit expensive but worth it and I have a 1010 blackbox standalone unit and am a fan of 1010 in general.
You definitely have a lot of quality modules but I wouldn't just march down this list because where you start after you have a few modules and a better idea of what you can and want to achieve I assure you will change where you end up.