I like this idea.
4: Plant barnacles.
So the 'order' would be UA then UP, then barnacles. Which would mean we've been working through the mysteries backwards.
Most of our interpretations depend on if we are either receiving messages deliberately sent to us or if we are just "hacking" into the internal operations and uncovering what they are up to. The image may be an attempt to communicate with us and we are too stupid to understand what they said or it's the first four lines of code in their operating system. I lean toward the hacking idea as I just don't think they are trying to send us a map. Could of course be wrong.
As far as the order from a "biological" perspective, if they are engineered for a purpose based on another life form (biotech) all we see the Barnacle/UA/UP (whatever the connection) doing is making meta-alloys. They like nebula presumably for the materials and possibly tied to the "self-repair" (corrosive effect) ability they have which maybe to help them survive in space while they do their Artifact/Probe thing.
Looking at a barnacle from the top it almost looks like it's "making" a UA/UP (center column) in a reproductive type of way. Remembering they are mostly on low-g planets, meaning lower launch energy, one idea I had was a barnacle would make a UA or UP which would launch and take a position in space looking for other barnacle habitable worlds which and plant more barnacles. Which made me think maybe in trying to describe that "in game" UP's might spawn in orbital cruise around planets, maybe Merope 5C if they are "outgoing" or other planets in the shell if they are "incoming". I've tried both with no luck.
I also think we may find that UA/UP are two modes of the same thing. The head texture is identical, the 12-part fragment end could be enclosed by the bigger end, "Probes" are illegal at stations despite them being (at the moment) more scarce and Artifacts known the disrupt stations (i mean seriously, UA's shut down a station and they aren't illegal to sell?), plus in the UP convoys the attackers call it a Artifact.