If you want to avoid spending money on R*S I may be the wrong person to talk to @toodee! I'm a huge fan of the Res EQ and would probably suggest that as the place to start with them, particularly if you're looking for a unique module that can really spice up a patch, especially drones, feedback patches, or things based on field recordings.
Re: my personal 303 one example of it patched up would be like so:
Metropolis CV => NTO
Metropolis Gate => Maths Trigger 1
Metropolis Clock => Algorhythm Clock
Algorhythm Channel 1 => Maths Trigger 2
Maths Trigger 1 => Quad VCA CV 1 (cascades to CV 2)
NTO Variable => Quad VCA channel 1
(optional) NTO Square => NCOM => Quad VCA channel 2
Maths Trigger 2 => VCFS or VCFQ CV, Q, or Slope in
Quad VCA channel 2 (mix of 1 and 2) => VCFS or VCFQ audio in
VCFS or VCFQ => out or to effects
There's a ton of variations that can work from there but basically you have a sequencer with a multi osc voice (though it's integer ratio subharmonic) through a filter that you can then add accents to. In the tunes posted here I'm using the M303, but in other tunes on my bandcamp, in particular Live Jams for Scotland, all the synth sounds basically follow the guide above.
my tunes: https://stevehand.bandcamp.com/