Does anyone have a guide on how the resistors are to be adjusted?
VCO: The VCO scales are both 1-2 o'clock, and the two other resistors are adjusted by ear (near mid position)
VCF: Both scales are at mid position, as the manual tells you to do. But should they be adjusted different? How to set them correctly?
VCA: Modulation null is set by ear, where it is quietest, near mid position. How about carrier null? Manual says mid position, nothing about how it should be adjusted...

The simplest way to set trimmers by ears is to tweak them until they sound right to you. The "clock" settings are ballpark. If you read deeper into the 4730 manual there is a more precise way to trim the filter. I think it's before the Design Analysis but I don't have it in front of me.

The problem is that I don't have enough experience to know what "right" is. I can't hear any difference while I'm adjusting them, because I don't know what I'm looking for...

If you can't hear a difference then it must be right. It isn't about what looks right, it's what sounds right to your ears. Your ears are more sensitive to hearing error for tuning and tracking then they are for amplitude and timbre. Don't worry about the VCF or VCA settings (if there's no audio bleed through you are good). When you follow Scott's tuning instructions, do the VCO's track? It doesn't matter if VCO B is a 4th higher than A when they are at 1 O'Clock as long as they track together and against another pitched instruments.

Trust yourself, Luke...