Welcome!
The most common eurorack beginner mistake is "Oops, all oscillators" and you're in today's lucky 10,000. 2x uPlaits, nRings, a percussion synthesizer, and an integrated synth voice. That's a lot going on all at once, and you don't even have all the utilities to use all of them (1x filter and no VCAs).
Step one is to walk back to a single voice and figure out what you need to make that work. You could just stick with that Doepfer synth voice module, nothing wrong with that, but if you want to part one out yourself, you need:
- VCO
- VCF
- VCA (1x per voice minimum, 2x is pretty close to necessary though)
- Envelope Generators (1x per voice is enough, 2x is pretty common)
- Modulation Sources to keep the sound interesting (somewhere between 1 and 1,000 of these ;) )
- Utilities to adjust those modulation sources (read: More VCAs)
With you being from Germany, you might be able to get a full Doepfer system for cheaper than most, on account of lower shipping prices. Doepfer doesn't make the flashiest modules, but they make extremely solid building blocks. Being fundamentally good but not so flashy means that it's on YOU to learn how to patch interesting. Were I to live vicariously through your wallet, I might recommend something like
- Doepfer A-110-2 (Basic VCO)
- Doepfer A-120, A-124, A106-5...Lots of options for the filter.
- Doepfer A-130-2 (Dual VCA)
- Doepfer A-140-2 (Dual ADSR)
Doepfer has fancier VCOs than the A-110-2, I chose it because it's the cheapest while still being something that can prove useful if you expand to a flashier VCO in the future (a basic VCO feeding the FM input to a fancier VCO is always nice to have). Like I said, there are a lot of opitons for the filter and it's hard to go wrong with your choice here. Your rack has an A-106-5, which is a clone of the Oberheim Synthesizer Expender Module's filter. Did you choose that deliberately because you like the Oberheim SEM, or music made with it? It's not a bad choice, just a curious choice for a first filter. The A-130-2 is a dual VCA, so you can dedicate 1 to your volume envelope and 1 to your VCF envelope. I'm not a huge fan of the A-130-4, because it has a shared gain control for all 4 channels, while the 2 channel version gives each channel its own knob and CV. Sometimes (cough-very often-cough) you wanna turn up the filter envelope amount without changing the volume of the signal. A-140-2 lets you define a separate envelope for volume and filter contours. Only thing I don't like about it is the lack of voltage control, but the A-141-2 (VC ADSR) only has one output for a whole lotta rack space. You can certainly use the same emvelope for amplitude and filter, many classic synths have done that. Or you can get 2x of the 141-2. Or you could break the completely arbitrary "all Doepfer" boundary I've imposed for no reason ;)
For modulation sources, the sky is the limit. THIS is what makes modular synths shine. All of those input ports can have something wiggling the knobs for you, so make sure you have lots of things to do that automatic wiggling! The most common modulation sources are LFOs and envelopes. You've already put 2 envelopes on your Amplitude and Filter. What other inputs might be interesting to wiggle around right at the start of the sound? If you go with a more complex VCO like Plaits, you could put an envelope on one of the timbre inputs. You could modulate pitch to give a little "scoop" or "drop" at the attack of the note. You could modulate your modulation sources! I love putting a high-rate LFO on the filter cutoff frequency, it gives the filter a certain "growl". What if you put that LFO through a VCA, and put an envelope on the CV? Now you get that "VCF Growl" on the attack, but it cleans up for the sustain phase! As you get more modulation sources, you need more utilities to handle them, though. You'll need a good colleciton of VCAs and Mixers to make the full use of them (Note that mixers for CV are often DC-coupled, as opposed to mixers for audio which are usually AC-coupled. Most mixer modules have some way to switch between these two modes, but it may require a little soldering).