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On the mixer, there a few comments :
1. The Doepfer A-138p is only half a mixer; you also need the A-138o for outputs.
2. Four channels is certainly not too much, maybe not enough as your system grows.
3. If you are using other instruments as well as the modular, you are probably better off doing the mixing on a "normal" mixer, outside of the rack. Eurorack signals are much higher than line level and it's easier to turn down the modular to line level, than to boost the other instruments to euro level. Eurorack mixers are also very expensive compared to normal mixers.

Sequencing from the Electron machines will surely work well. I don't know the Doepfer MIDI-CV interface but it does not have very many outputs, so you will quickly reach its limits. And by quickly I mean immediately: you could control one voice with this. You might look at some options with more outputs; Expert Sleepers make some very popular options.

More generally, this is small case, so you would do well to consider the size of the modules you are putting in there. There are small alternatives for many. Mostly obviously, the multiples have no controls, so why not choose a 2hp sized version? Many manufacturers make these. Same question about the ADSR and the attenuators.

As it stands, this set up is a one-oscillator monosynth. For this purpose you need two envelopes : one for the filter and one for the VCA, but you only have one. If you want to combine envelopes with your LFO you also need a CV mixer. The Happy Nerding 3xMIA or Befaco A*B+C are good options but there are many others.

On the other hand, can this do anything your Analogue Rytm can't? That's a genuine question -- I don't now the capabilities of that machine. Did you consider any semi-modulars? Moog Mother-32 or Behringer Neuron are much more capable than the rack you present above, and also cost less. I would consider a bit more what you want to add to your existing music, and start your rack from that.