We should trade, but carefully, we should have some parameters:
We do not actually use anything they give us, instead we reverse engineer the technology to develop our own equivalents. (this will help keep us from being tech-dependant on them, or from using technology that they have sleeper protocols within, keeping us free from their influence)
We do not tell them about Hive mind. They don't seem to be too far ahead of us, as they needed to manually grab a primpsk. We should be able to keep the hivemind secret, and eventually expose them or their homeworld(s) to our assimilation. It will simply look like part of the organic system of the planet, rather than an all controlling overlord.
Every interaction should be used as an opportunity to pollinate them, in a way that seems benign. We should leave all infections as sleeper infections that appear benign, and unalarming. Only activate the full-fledged-infection once we have extensively sleeper-infected them, and plotted out their holdings. The last thing we want is for them to be able to fight off/quarantine the infection. A flip of a switch that converts their empire would be much more effective. Our mode of infecting them would probably work best if it rode on them/their ships/the materials we give them and first infect their homeworld(s) biospheres.
Glean as much technology as possible from them, diplomatically haranguing them if they are stingy.
Request an ambassador(hostage) that will stay on our planet, offer a primsk in return (one that is made such that they cannot find Jethro in it, maybe just a preprogrammed mind, but no infection, make it rather dull, and don't worry about ever getting him back. Analyze the ambassador as closely as possible, if necessary, dissect him and reverse engineer their organic matter (if it is not DNA based or familiar) and create a doppleganger that can walk around and wave at the skies, in case they are watching. We need to determine how their biology works, so that we can develop a manner of infection,(if they aren't dna based)