Find a Eurorack dealer with a nice return policy. It's going to take a week to figure out if you like the workflow (assuming you're going with a complex sequencer).
I own a Westlicht. I like it. But be sure it's built by someone who gives a damn.
I also own a 1010 Toolbox. I like it too. It's easy to program. But it lacks a lot of deep features and some of the updates have been kind of crappy IMHO.
As far as simple sequencers, I own a Pittsburgh Modular Microsequencer. I hate that little bastard with a passion.
But the Befaco Muxlicer is pretty intuitive and useful in comparison.
My micro Ornaments & Crime has a sequencer mode built into it that is very nice for its size (it can also do envelopes instead of gates.
I also have a Noise Engineering Digitalis Mementic... which is a great little sequencer for improvisation.
I'd buy one complex sequencer to start and one or two simple modules that can be triggered or sync'ed by the main sequencer.