Hi Nickgreenberg,
Oh that's great, then the most important element you have it already ;-)
Well... what you could consider then isn't really a pure sequencer (well... a chord sequencer) but might add some serious added value, which is the Sinfonion from ACL. If you think the Vector is a beast (which indeed it is if you just look at the point of being a sequencer) than the Sinfonion is a beast-cube (beast to the power of three) or something like that ;-)
That might be a real addition to it. Another interesting idea might be, as "simple" as it sounds, to add more drum variation, the Erica Synths - Drum Sequencer. Or yet another alternative the Erica Synths - Black Sequencer.
If you don't mind to think outside of the box (your Eurorack) then you might want to consider the Erica Synths' new drum synthesizer Perkons HD-01, brand new, not available yet :-)
Ha, ha, I have no idea why I come up with so many Erica Synths devices. Well there are tons of other good sequencers, you mentioned already yourself that list of sequencers made by Martin Doudoroff, it's rather a matter of money and HP space then lack of sequencers ;-)
Though please have a look at the Sinfonion, that really might be a good "add-on" for your already existing Vector. Good luck and kind regards, Garfield.
For review reports of Eurorack modules, please refer to https://garfieldmodular.net/ for PDF formatted downloads