I'm also considering adding a drum sequencer, in- or outside the rack.
May I ask why you want to move the sequencer inside your rack? Is it purely the form factor?
On paper, the Beatstep Pro has somewhat the same functionality as the Erica Synths Drum sequencer (I believe difference being that Drum Sequencer has a few more tracks and accents while Beatstep Pro has two cv/velo/gate sequencer which you could also use for accents of course), while costing 1/4th of the price of the Erica Synths one. Also the workflow seems quite similar.
Just curious.
Besides a drum sequencer where you'd program your own sequences, I find the Mutable Instruments Grids (or any of its clones) usefull to have as interesting accents or some extra background voices. Also it's really easy to dial in snare fills and funky hihat patterns. Grids is also not too expensive so maybe it's nice to have besides a dedicated drum sequencer.