I'm now investigating into some VCA/enveloppe and/or LFO/enveloppe (any input appreciated).
For VCA's, my first one was a quad VCA from Intellijel, I still like being able to adjust the response between linear and exponential as well as the mixing possibilities. 4 VCA's was more than enough to start messing around in my first rack, I could have done with even less at the start. That being said, consider that a VCA is not only for audio but can also be used to control modulation (=cv) amplitude, so it's not necessarily 1 voice = 1 VCA. And on the other hand, some modules like Plaits, Plonk or Basimilus Iteritas Alter have integrated VCA's which are amazing space savers. Mutable Instruments Veils is another option similar to the Intellijel one, there are also many others so take your time to pick a module. Since you played with VCV, did you try experimenting with using VCAs to control CV modulation or even AM synthesis (amplitude modulation) ? Some practice using VCA's in your VCV patches should give you an idea of how many you like to use. If you really can't decide, start small, I suppose.
For LFO's, Garfield convinced me to get the Erica Synths Octasource and I'm grateful he did, it's loads of fun. The only "drawback" is that it looks like a simple module but it actually took me time to learn how to best use its particularities, clever patching is everything here and that's not easy when you're starting out (wasn't a problem for long though). Oh yeah, it's also not on the cheap side, albeit worth the asking price IMO. Another option I see recommended a lot is the Batumi, looks like a good module to me, less on the crazy side I think. In my rack, I also have a Mutable Instruments Stages which can be configured to offer up to 6 LFO's. The amount of options here is simply overwhelming, the best advice I think I can offer is again, take your time to select what suits you best. That being said, I don't think one could go wrong with any of the options mentioned.
For envelopes, I haven't tried enough options to really recommend anything, but I'd say decide first what sort of envelope you need. For example, I quickly realized, before I got into modular, that I'm generally fine with AD envelopes and rarely need a Hold stage (which stays open while the gate is held) or a full ADSR. I picked the Stages to be able to select the envelope type per patch, that kind of flexibility is really nice.
I feel like at this point I should mention Maths since you are considering a rack with more space. Maths is a large module but it's definitely worth it if you can afford spending some cash and 20HP on it. It's an amazing tool to teach newcomers about what I call "clever patching techniques": amongst its many uses are being an LFO or being an EG but there's a video out there (I think by Loopop) of it being used as sort of a Subharmonicon so really, sky is the limit. Also, you might not need that A-171-2 if you end up getting a Maths.
As this rack also serves an educational purpose I still hope I could get started doing 'something' with these few modules modules and get a taste of what's missing from this point.
Do you think I still can enjoy the basic concepts with this setup before going further?
Sure, if I were you I would even start with only one voice to begin getting a feel for it, you can always buy more later. Full disclosure, I didn't, but I'm definitely greedy :) You have the option to sample the voice into the DT and make another patch if you can live with sacrificing a DT voice for a while. I think that for the learning part of the experience, getting a Disting is a great idea, you can try many types of modular functionalities with it and discover which ones are worth getting their own module.
Oh by the way, what is the A-183-3 for ?