'K so time to keep going with this. My next topic: Dreamselves. Right now I am specifically concerned with how we decide who ends up with what. So, let's begin.
Overriding concern: Domains.
At least one domain is DEFINITELY linked to a particular planet: Space. It seems to be a definite constant that the First Guardian wakes up the Space player, who lives in a tower much like their Prospit tower and meets the WQ and sees the clouds and is generally all bright and happy and quickly taught to align with Skaia.
Light meanwhile, shows that Domains are not ALL linked to planets, as Vriska is Prospit and Rose is Derse. For this reason, I suggest that Breath is also not necessarily aligned, despite Tavros and John both being Prospit dreamers. However, for symmetry reasons, I suggest that just as Space always gets shunted to Prospit, Time should always get shunted to Derse. It just feels appropriate.
Next concern: Interplanetary Balance
We have seen two sessions, one with four players. When this happened, two were assigned to Prospit, two to Derse. Whenever there is an even number of players, therefore, we should definitely keep this pattern going. However, we've also seen a thirteen dreamself session, where the balance was seven Prospit dreamers. However this definitely isn't indicative of anything. It may be that the balance always tends to Prospit when necessary (furthering the fact that the game favors Skaia, not the Horrorterrors), or it might be randomly decided where the odd player out will go. We should make a decision here as well.
Third, optional, concern: Gender balance
In both sessions we've seen genders are evenly represented on both planets. It might be worth our while to code for this, then. Obviously it will not be possible or wise to force players to split down the middle on gender (that might be canonical, but it's not fun), but in the event of say, five boys and three girls it would be wise to assure that we don't have every Prospit dreamer be a boy or something silly like that. Just food for thought, and as I noted, this is an optional concern. I just thought it was important to note.