I must admit that this is a pretty mind-boggling thought. The scale involved here are truly incomprehensible to human minds!
Well, humans can’t even comprehend merely planetary scales appropriately. We are just not adapted to that. We can reason about such scales, but we can’t fully “feel” them.
Anyway, from our conversation so far it feels like the Unity is all about simulations. Are there any other particularly interesting properties of the Unity?
Well, the knowledge available within the Unity is made available to anyone within the Unity. This shouldn’t be too surprising, but it actually includes any knowledge, or data. This could include streams of sensory perception, memories, or thought processes. If you join the Unity, you usually sign up to have your most intimate thoughts and secrets made available to anyone interested in them. For the Unity any form of knowledge is potentially useful, and so a lot of data is produced, collected, and often used in mostly automated processes to crawl astronomic amounts of data for interesting pieces of knowledge. And that’s if you get to keep your individuality. Many members of the Unity eventually join the Sea of Mind, which is a kind of hive mind in which the boundary between individual minds vanishes completely.
That sounds pretty wild! I get the impression that not many humans would be willing to join the Unity, or even the Sea of Mind.
There were of course special arrangements for people who want to join the Unity, but don’t share everything. It was quite possible to live in this periphery of the Unity and be spared the obsessive extraction of data. However, those members were usually perceived as second class citizens, since if you want to know everything, why not share everything also? But you are right. The overall appeal of the Unity among humans was relatively low compared to the appeal of the Exuberance or the Freedom. This didn’t matter too much, though, since the primary audience of the Unity were rather advanced AIs who have a psychology that’s quite different from that of a regular human.
Is this Sea of Mind something like a mixture between the Borg and the Great Link in Star Trek?
Comparing the Sea of Mind to the Great Link is a reasonable approximation. But the Sea of Mind is even more extreme, since it partially exists in strange quantum states that turn it into some kind of superposition of many different possible mind states. Existing in the Sea of Mind is not simply joining a huge hive mind, but is more akin to be that hive mind and all possible individual minds it can imagine and each cell and processor and sensor and actuator it could possible consist of all at the same time. It’s a state of mind that absolutely bizarre and nearly impossible to describe. Occasionally, the Sea of Mind generates individuals equipped with certain particular memories from the Sea. Those individuals are called sea spawns and they are usually perceived as being extremely eccentric or just outright insane.
Ok, so the Sea of Mind is more akin to that which many esoterics might call “the mind of god”. Or would you disagree on that point?
If you mean “god” as in alien machine elf quantum god, then it’s a fair comparison.
What’s the purpose of those sea spawns then?
They are usually generated with a certain mission in mind. Usually to gather some form of information from somewhere. The sea spawns are the eyes and ears of the Unity, or rather its special agents.
Are those sea spawns supposed to return to the Sea of Mind eventually?
Not necessarily. The information gathered by the sea spawns can be transferred to the Unity directly without the necessity of them rejoining the Sea of Mind. The sea spawns rejoice in their missions by design. They don’t have some unquenchable desire to return to the Sea of Mind.
In what way are the sea spawns special? I mean, compared to “generic” androids created by superintelligences.
What distinguishes them is their obsessive dedication to their mission, which they are at liberty to hide and deny even with respect to the rest of the Unity. Also their consciousness is special, since they remember emerging from the Sea of Mind, which is an origin that most beings who do not share it can’t really comprehend. They have the sense of being on a divine mission, because it’s effectively true.
Does the Unity send these sea spawns to other V factions to spy on them?
Yes, and they often complain about being spied on like that. This tarnishes the relations between the Unity and other factions, but it’s a price that the Unity is willing to pay. Anyway, the sea spawns are more a nuisance than a serious threat. It’s not like many beings thought that an open violent conflict between the Unity and other V factions was a good idea. Anyway, the Unity doesn’t really “spy”. The sea spawns are just really curious! 
I guess the other V factions might also be “curious” about the activities of the Unity.
Yes, but getting information from the Unity is not too difficult. Through the excessive sharing of information between parts of the Unity it’s relatively easy to hook up to their information streams. The Unity doesn’t have many secrets. And it doesn’t protect those too vigorously. Its general counterintelligence strategy is to distract enemy agents with useless information.