Hi Metal_Serra,
Where shall I start? ;-) Perhaps with a big welcome into modular synths? :-)
Fun putting aside, please be careful when you plan a modular system. May I ask why you "must have" a modular synth? What is your real reason to have one? If it would be anything into the direction of: "Because everyone has nowadays one" or "Because it looks cool" or something like that, you might wonder if you really should get one. No matter how carefully you plan, how much time you read in the evenings and nights about it, preparing yourself, etcetera, a modular synth, there is no way of getting around it, is bloody expensive. And once you are hooked into it, there are things going to happen to you, you start thinking of selling your car, house, partner, kids, whatever you can find to sell to get more gear, more modules and more rack space. Naturally I am kidding here about partner and kids but the thought of selling your car or house shouldn't surprise you once you are into this! :-)
Okay having said that, just as a warning, so you can't claim, I haven't warn you ;-) Having said this all, a modular synth is fantastic but you need to be willing to let it cost a fortune. Think in several thousands of dollars/Euros as a very minimum, likely a factor "X" of that.
That's one thing, the other thing is, that you might want to take this a bit slower first and get a better conceptual thinking of a synthesizer in common. My way of doing this was by getting a Behringer Neutron, it's reasonably priced, so if you discover after that exercise that modular is nothing for you, at least it didn't cost you an arm and a leg! The Neutron is nice to start with because you got all the basic components in one device with quite a few patching possibilities. Components like: 2 VCOs, LFO, filter, two EGs (envelopes or ADSRs), VCA and it even got: a delay, overdrive, sample & hold (S&H), slew rate limiter and two attenuators.
Don't think because of all that "basic" stuff there is no fun with the Neutron, no the opposite I would say. With the Neutron you can test basic functionality, get surprisingly quite some nice sound out of it, and it gives you a "pre-tasting" of modular synthesizers. It's a kind of test for yourself to see if you are really into modular synths or not and it's a cheap way to discover it. If you go directly into modular, it's very costly and if you don't do your homework right, it's going to be a frustrating and expensive experience that might go wrong :-( So I would like to avoid that, if I would be you.
Don't get me wrong here, I don't want you to think modular synths sucks, no it isn't but you have to be very well prepared, very sure about this. Once you are (and my advice is to have that tested with for example a Neutron), you can go all the way with modular synths :-)
Okay, let's put that all behind us, let's say you are very sure about this, checking your E-mail further:
It's good to see you got already a guitar with lots of pedals. I recently got the Source Audio - Ventris Dual Reverb pedal, what a fantastic pedal that is! I don't have a guitar but I am using this effect pedal/module for my modular synth and wow, what a beautiful sound you can get with that Ventris! So having a few pedals wouldn't harm to lift up your sound a bit :-)
The Digitakt and the Circuit Mono Stations are nice too, so that helps you and since you got those already, you might need indeed not straight away a full blown modular synth to get started.
Still, my advice would be to look into a bit bigger rack. You might not want to believe this at this stage but you can't have a big enough rack. Go for at least 3 * 84 HP or 2 * 104 HP as a real absolute minimum. Even that's too small but for your case, it might be a good start indeed.
What I like of your "design" is that you left a lot of space empty, that's good. Don't straight away fully plan it because you need space "to grow" with your experience and your changing needs within modular synthesizer. So in your above example that's enough reserved space or better if you would go for a 3 * 84 HP rack, leave at least one row empty to start with.
Going into your planned modules. STO and Plaits are good modules that also can give a good benefit to those who just starts in modular synth. However modules like Stages might be good but to start with? I would advise against that. Start easy and simple, grow in experience and then look more into those "fancy" (or a better word is perhaps "complex") modules.
Back to the roots: My question stands... are you sure you are ready for modular synth? You seriously might want to get started with for example a Neutron first to create an appetite for modular and test your likings.
If you are now already very sure that you want to go into modular then welcome to modular and enjoy :-)
Good luck and kind regards, Garfield Modular.
For review reports of Eurorack modules, please refer to https://garfieldmodular.net/ for PDF formatted downloads