I noticed that you seem to have quite a lot of experience with the Disting. I often see o_C being mentioned as having a similar use case, how do both of them compare?
In some ways the Disting and O_C are pretty similar in that they have a bunch of different algorithms for all sorts of different use cases. And yet, they are pretty different...
For one thing, the O_C's processor isn't as powerful as the Disting, so it generally doesn't handle audio signals well. It can do some audio, but it's fairly lo-fi (the audio is downsampled). For example there's a lo-fi tape delay effect in one of the firmwares but it "at a sampling rate of 2kHz for about one second. Incoming signals are down sampled to 8 bits of resolution." That might be what you want sometimes, but it's definitely not a "go to" delay. The Disting on the other hand handles audio no problem and can do higher quality effects, VCOs, and sample playback.
AFAIK most O_Cs can only output a specific 10V range, so to be able to do bipolar CVs (like LFOs) as well as unipolar (like envelopes) they had to compromise and at the hardware level set the total output range to something like -3V to 6V. Often LFOs are -5V to 5V and envelopes 0V to 8V-10V. So you never get as "deep" a modulation as you can typically get from other modulation sources. Typically this isn't a problem but I have noticed using it as an envelope tends to lead to quieter sounds and then you have to mix appropriately or use an amplifier.
To address that -3V to 6V limit, Plum Audio made an O_C with variable output range (VOR) that switches on-the-fly between -5V - 5V and 0V - 10V in the firmware depending on the algorithm, which makes it behave like a traditional CV source. I don't own one of these but it's a nice selling point so I'd definitely consider the VOR version of the module. However, not all firmware supports VOR (yet) so that's something you need to be aware of if you are trying out different firmwares.
The O_C is also open source and people have made various forks of the firmware, which has been fun to experiment with. I currently really like the Benispheres firmware. It's got a good selection of algorithms and they are all pretty straightforward and intuitive to use, generally without consulting the manual. The stock firmware is fairly complicated though, so expect to spend a lot of time looking at the manual and scratching your head, but there's some gems in there too so it's worth a try at some point. If you are into software development, you could even make your own fork of the firmware and make the O_C do something new.
With the Disting, you've got the slimmer mk4 version and the EX. I started with the mk4 and I don't regret it. I get a lot of mileage out of it but I have to say the mk4 is a pain to use. It's so much functionality squished into a small space with only one encoder and a rotary knob. The UI is basically a big compromise with tons of pressing and turning to dial in each parameter one by one. It's time consuming and tedious. Every patch I try to decide on the one thing it's going to do and set it up in the beginning so I don't have to worry about it mid-patching. Menu-diving into the disting mid-patch isn't much fun.
The EX is definitely a lot better in the usability regard with the nice screen and more knobs, but with both models there's so many algorithms and they all have so many features it's practically impossible to use without the manual right next to you. Eventually you find a few algorithms you really like and I remember enough of how they work I don't have to consult the manual for those anymore, but it was a big learning curve. Between the need to consult the manual a lot and the menu-diving, I can see why some people don't like the Disting. But for me it's been really great to try out new ideas and learn more about what you can do with modular.
The Distings are a closed platform though, so only Expert Sleepers (AFAIK) ever releases firmware for it. But it can do so much, especially the EX, so I don't really care.
So in summary:
O_C is focused on CV and not so good for audio. The CV output range is somewhat limited unless you get a VOR version. The Hemispheres-based firmwares are easy to use and you typically don't need a manual, so it's quick to dial in settings and "play" it on the fly. The stock firmware is interesting but suffers from the same sort of usability problems as the Disting.
The Distings are great with both CV and audio. The algorithms cover more territory (especially the EX which really does have an incredible amount of powerful functionality), but it is a lot harder to use (the manual is practically required) and not very hands-on the in the middle of a patch.
Honestly I recommend both and I probably won't ever sell off any of mine, but you probably should start with one and take it from there. Hopefully this info helps make a decision.
Is it worth considering the 4Robots plum audio module over the golden master, and get the intellijel line out?
Getting the 4Robots O_C (which has VOR) instead of the Golden Master seems reasonable if the O_C sounds like a good fit for you.
If you're getting an Intellijel performance case, I think it's really nice to get one of their 1U output modules and connect it directly to the jacks on the case so you use those for output. Note the Headphones 1U module does not connect to the case's output. You need to Stereo Line Out 1U or Stereo Mixer 1U (and I remember seeing in the manual you need a second-generation case or something, but unless you are buying older used equipment, I doubt you need to worry about that).