From what you say I understand that you will use MIDI to take both clock and CV from the computer to the case. You can use VCV Rack to generate the main clock and bring in some CV signals to modulate. You can start like this, of course, but keep in mind that:
-Managing the knobs "physically" is like a drug, once you try it you won't want to use the PC for it.
-To experiment in the field of generative and ambient, an effects module will give you many possibilities. I wouldn't know which one to recommend, since I'm not really into that field yet.
-Sooner rather than later you are going to need EG's, LFO's and VCA's, apart from additional utilities. Prioritize them before additional voices.