Hi farkas. For output to pedals look at:
ADDAC200PI Pedal Integrator
I wanted the ADDAC but it wasn't available at the time so I ended up with knob.farm Ferry which is fine.
There are many other pedal interface modules which you can find here on MG including this "full-feature" module, Merge, from Adventure Audio:
Strymon makes one as well (AA.1 Amplifier Atenuator)
For input I use CG Products Pre:
For input you are probably all set with the Doepfer A119 (seems perfect, pre-amp, envelope follower, and comparator).
But check out some of the other modules from CG Products; the Peak + Hold, Noise VCA, Delay 1022, etc. With the Peak + Hold > Noise VCA I can get very good percussion sounds with guitar as input (or really anything as input, basically pinging the filter). I have an envelope follower from Grp.
I have done a lot of stuff with guitar and the modular but I should say I have only played around a little running guitar through the modular. The guitar has been on a separate track and I haven't really recorded anything with the guitar going through or modulating the modular. You can use the signal for FM with VCFs, VCOs, etc. and go crazy running the audio through Clouds, Arbhar, Nebula, etc. But I find I haven't utilized any of that when I record tracks, I mostly use the modular as the 'rhythm section' or I'll comp chords and let the modular do its thing. Maybe now you'll have inspired me to utilize it in this fashion, I hope so!
Let me know if you discover anything good.