Hi TF - welcome back to music!
Before people chime in to offer suggestions, I can't help but notice that you appear to be conflating two products - KeyLab MKII and KeyStep. The KeyLab MKII is a MIDI and CV controller, plus a control surface for your favourite DAW/synth software and does not have an arpeggiator or sequencer, while the KeyStep is also a MIDI and CV controller, but is geared towards sequencing and arpeggiation. The KeyStep keyboards are excellent for sequencing and come highly-recommended if you want to concentrate on programming sequences without a computer as opposed to using a DAW (which I think is the approach most people take these days). If you want to use a DAW, then the KeyLab MKII is an excellent controller/control surface. By their nature, almost all DAWs will act as a sequencer, and most (but not all) will have an arpeggiator. The AKAI controller you mention has an arpeggiator, but does not have a built-in sequencer.
If you can clarify what you're after workflow-wise (e.g., standalone sequence programming vs. DAW), then I'm sure the group will be able to help.