Hello megoth, ive been doing this a couple of years now, thought i'd stick my head above the parapet :)
The main advice you'll get from other users is to not do drums in rack as its too much cost for little gain. I'd recommend looking into something like the Pulsar-23 for a good drum machine that can interface with eurorack. It only handles 0-10v instead of -5 to +5 so you'll need additional modules to offset/attenuate as necessary. But, it'll still be a lot cheaper than whats proposed here.
That being said drums in eurorack is fun! And even better when paired with modulation, so I think it would be good to know what other modulation your planning on getting in your other case. The key to good drum sounds is decent modulation and utilities otherwise your voices will sound static and boring. Things like sample and holds, clock dividers, shift registers can spice up velocities and gate sequencies. Random CV is also great for sound design- you can get this from a sample and hold and noise source. Noise in particular is very useful- it can also be used to create percussion!
And with modulation you'd need VCAs. Super useful for modulating modulation. And also accent creation. In conjunction with sample and hold and you can extract velocities from modulation! if you attenuate and rectify before hand you can get it to play nicely. And rectifiers open up a world of possibilities - when combined with slew you can get an envelope follower which is great for sidechain effects. I'd look into function generators like schlappi boundary or make noise maths. The ultra kick/perc has this built in but doing it in other modules has its benefits.
You'd surprised at how much mileage you'd get from an Oxi One. I had one for ages before I sold it for a Hermod+, which is an insanely powerful sequencer. I would question why you would need 3 sequencers, and just stick with the Oxi for now. See how you go with that and properly get to grips with its functions. It's a mini modulation centre in itself!
Havent even touched on ringmod, effects, mixers, clock dividers, more utilities etc. There will come a point when you wish to do something but can't because you dont have the right utilities. Also a good way to save money instead of having dedicated modules (already touched on building random generators and envelope followers, there is a ton more).
Finally you may wish to consider to get something not behringer. Eurorack is a boutique business, and a massive company stealing designs from much smaller companies, is not a good thing.
Enjoy the build!
TLDR/EDIT:
Essentially do drums outside of rack unless you suplement with all the things that makes modular, modular. If you do them in a rack where your only modulation sources is just a sequencer, youve just spent a ton of a money on essentially a very limited drum machine. Manually drawing accents and swings is fine, but in the modular world you can automate to get far more inspiring patterns with a turn of a knob. Drums only becomes killer when you pair it with modulation :)
EDIT 2:
I know youve got 2 ochds, but you may need something which syncs. And mixers, analog logic functions like min/max to make the wave forms more interesting than triangless.