depending on what you want from a rack then a trigger sequencer like steppy may be useful immediately - if the track is predominantly percussion, for example
in a general purpose rack of this size where I would advise keeping to a single (melodic) voice, pams can adequately cover trigger sequencing - as there is not that much to trigger, as well as envelopes, unipolar lfos and looped quantized random cv for generating melodies
at some point you may want to have more control over over melody - and I would expect this to be before wanting a trigger sequencer - in which case a melodic sequencer not a trigger sequencer is what you would want
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities