Question

I am using AudioBox 44, Studio One Artist 3, and a Yamaha Midi keyboard controller.

Answer 1

Studio One does not have a proper "Step Sequencer", however the piano roll can function in much the same way.

Set your loop.

Set the grid quantize value or "Beat" value at the top of the piano roll

Enter notes by clicking in the Piano roll for the Impact pad and bar placement you would like. Once you start using it you will understand how similar it can be to a step sequencer.

Answer 2

There is a step record function accessible on the Edit panel. Once you have that open, you should be able to step record as in any other DAW. (You need to see how Impact is set up as to which keys on your midi keyboard or that your drum pad is properly mapped to trigger the impact samples). You can also search "step record" in the manual for more information.

Answer 3

A much better approach is to use a proper pattern-based step sequencer VST that can directly drive a drum-pad (ie. Impact) or synth (eg Mai Tai) from inside Studio One.

It's called B-Step. Check it out here:
http://b-step.monoplugs.com/en