Building a drum machine in Eurorack is a VERY expensive proposition. You have to recreate all the parts of a drum machine out of individual Eurorack components. There are manufacturers that do make self-contained drum voices. But then you're basically back to where you started from.
I would consider it IF I wanted to get down to the very roots of the sounds and modulate various aspects of the sound that you can't with a normal drum machine. But if you go that route, you're basically building drum sounds from scratch: VCO, VCF, VCA, envelopes, and whatever else you want to throw at it.
If you want absolute control over your percussion and play all of it live, then you're going to need several of the modules above in duplicate. You're also going to need to mix it all... ON TOP of anything else you're doing in Eurorack.
Some deep thinking on what's practical, affordable, and if you really want to go this route. It would be far cheaper to create sounds one-at-a-time and then simply record them into a sample playback module once you're happy with the sound.
-- Ronin1973
Ronin1973 - thanks for the thoughts. Really helpful for sure. Here's my question (again, not knowledgeable here) - why can't I just use the drum trig outs on the Beatstep Pro for each of the drum modules I have here. I could use one of the gate/pitch outputs for the Syncussion as well to get pitch control. If I had another sequencer in here, perhaps the Erica Drum Sequencer then I could use that instead - right? Or would I still need VCAs for that? Also, I hear you on the mixer but I have an Erica mixer in that setup - 6 channels, why doesn't that work?
My plan wouldn't be to play this live but for sound design that I will sample into my digitakt or ableton and use from there. I assume I could create loops and record them too for arrangement later. Thanks so much for helping me!