Hi Metal_Serra,
Yes please be aware that this forum has a kind of "bug" that if you write too long messages, I mean if you need long time to write a message, that there is likely to be a time-out and you loose everything you just wrote :-( It's pretty frustrating, I have mentioned this already to the owners of this website but not sure where exactly problem lays, it looks like it's not an easy problem to solve. To me it looks like a time-out timer issue for this website but that hint didn't seem to help ;-)
So the only thing what you can do, at least that's what I do, since I also lost a few times quite long texts I prepared to write to people, is... just before you click on the send/submit button is that you select the entire text you wrote (control-a) and do control-c (copy). So if the submit goes wrong because of the time-out, at least you can login again, reply to the message you were busy with, and control-p (paste) it back in there. Still not nice or perfect but at least a workable workaround.
All right, so you are going full for modular system then?! :-) Well, welcome here at modular grid and welcome into the financial black-hole :-) But you seem to be capable of keeping yourself under control if it comes to buying pedals, so let's hope you can do the same with the modules.
All right 2 * 104 HP doesn't sound too bad and since you got already here and there a few bits, to start with, let's hope that's enough for the moment. But then your next question is a difficult one... only 3 modules to start with? Let's have a look at a minimum classic setup:
2 VCOs, if you like a ring mod one of that too, 2 filters, 1 LFO (2 would be better), 2 EGs, 2 VCAs (one linear and one logarithmic), mixer and audio input/output module and then we are not talking yet about some utilisation modules, other kind of fun stuff, just the pure basic stuff. That are already 2+1 (ring mod)+2+1 LFO+2+2+1 mixer+1 audio = 12 modules, as a minimum...
Now I understand that you got here and there already a bit but how you want to reduce from 12 modules to 3 modules is not very clear to me. To me that sounds you want to do the impossible ;-) In my above example you can skip the ring modulator for the moment, that makes it 11 modules. Let's say you go first for just one filter and one EG as well and let's say you start with a logarithmic VCA only as well, then you still need as a minimum 8 modules... you could go down to 6 modules by only having one oscillator (then you might not need the mixer as well) but by reducing to so less modules there isn't much modular synth fun left if you would ask me...
So with reducing to 6 modules you are looking at this: 1 VCO, 1 filter (VCF), 1 LFO, 1 EG, 1 VCA (log) & 1 audio output module.
Yes, this is theoretically possible but I would strongly advise against it, keep my initial basic setup of 12 modules in mind, you can tweak there around with one or two modules but don't go down to only 3 or 6 modules, I don't think that makes sense.
So my offer still stands... try this out first with a Neutron :-) Even if you are deep into modular, the Neutron still can be used. I regularly still use the LFO of the Neutron, very useful one and the dual VCOs aren't too bad either.
Be careful with what you are planning, it sounds a bit scary to me, good luck with it and kind regards, Garfield.
For review reports of Eurorack modules, please refer to https://garfieldmodular.net/ for PDF formatted downloads