Ok, that’s not really true. 
I’ve got a couple of really rough months behind me and was able to just briefly check lines once in a while. I finally had the time to read through this thread properly, and while doing so, I remembered many more details. So let me add some more to what I have written above and to what @Jet wrote earlier (and btw. @jet feel free to add anything, or correct me if I’m remembering things wrong)
Before starting to collect sounds we discussed various approaches. We thought that it might have been interesting to define a series of keywords and collect sounds matching these. Originally we intended there to be some sort of concept, but we both had various things holding us up at the beginning, plus the time zone difference didn’t help, so we didn’t work on that part as much.
Still, we got a nice list out of it, and I guess there was some fil rouge in it after all anyway. We split the samples into roughly 4 categories: synthesis, field recording and ambiences, percussive sounds, and noise. The tonal ones were to match a scale we had agreed on previously. @Jet worked with a major scale and I did work with the relative minor. For some reason we liked the idea of basing everything on a 9th chord.
We produced a lot of material, like others here, I’m sure we could at least get one or two decent tracks out of the stuff we haven’t used.
Once we had all the samples, we decided who would start (online coin flipper did the job for us, IIRC) and decided roughly what the layers should be and which sequence we’d create them.
We decided to start from a basic harmony track, then add bass, percussions and then move to the higher-register tonal parts / melody. @jet suggested that we’d always make both a tonal track and one that would only use noises, and non-tonal sounds. This worked very well, helping to keep both aspects in a balance as the piece developed.
We had never worked together, the collab spontaneously happened thanks to lcrp, but we roughly know what kind of music the other one was making. We did not really agree on a style or genre, and just let things happen. The first layers came out quite drone-heavy, and ambient-like and we decided to just stick to it.
Towards the end my private life and work, got a bit messy. @jet did the final mix and sent everything off (Thanks again for taking care of that!)