So how exactly do the 7 gates work, and would there be more gates the more people in a session?

In the Kids’ Session, the first Gate connects somewhere else in their World- The second, to another Land. Third, arguably to either another place in their Land or to another place in the next Land, Fourth to another land. Fifth and Sixth follow the same pattern with the last Land, and the Seventh leads to the Lair of the Denizen. This method makes it seem like the number of Gates in a Session is the (Number of Players * 2) - 1, which would leave it at 23 for the Trolls- However this doesn’t seem to be the case.

While the Kids’ Gates are all up on their Houses, and the Troll Sessions have Gates on top of their houses as well, there are also Gates and Return Nodes scattered through the Land Itself, some of them leading to other Lands just like the Gates above the Player Houses seem to, just like how Tavros’ Second Gate was over an unrelated windmill. Vriska also comments that Tavros’ Seventh Gate also leads to his Denizen’s Lair, an the Frog Temple’s structure implies there are always only Seven Gates above the Houses. This leaves the full structure of portals interconnecting the Lands a bit messy and very much unknown in any Session with less or more than 4 Players. Maybe the ones above the houses all link to different Lands instead of different parts of the Land? Or maybe they work the same, with extra ones scattered over the planet? No idea.

It’s not arbitrary, however- There are Seven Gates for a reason. Some say they represent the Seven Chakras, also known as Gates, with the Eighth one, Enlightenment and Unity with the Universe, being Skaia itself. I’m not quite sure if this is confirmed Canon by Hussie, however, and they could also reference the Seven Heavens of many religions, including Gnosticism, which Homestuck references directly in several occasions. And given the fact the Universe and ultimate objective of SBURB is a Frog, with Abraxas being the “Lord of Toads and Frogs”, I’m more inclined to believe they’re more of a reference to Gnosticism, but who knows! Either way, Seven Heavens or Seven Chakras, the Gates are most definitely symbolic, which implies that yes, there’s always 7 of them.