...just how many characters are in homestuck...?
A lot.
And the shipping isn't just as simple as "they love each other".
There's the whole "quadrant" system derived from the troll character's culture.
Basically, Matespritship (the heart/"flushed" quadrant) is essentially just human romantic love, as typical as it gets.
Moiralleigance (the diamond/"pale" quadrant) is essentially a guardian relationship. Characters in this position can still possibly become flushed, but the general gist of their relationship dynamic is that they exist to keep each other grounded.
Kismesistude (the spade/"caliginous" quadrant) is essentially "passionate hate". You essentially would love nothing more than to see this person dead, but you also feel a strong and passionate sexual attraction to them.
Auspisticism (the club/"ashen" quadrant) is a three way relationship, where two people hate each other, but a third person exists as a "mediator", making sure the other two have their hatred controlled, essentially making sure they don't go into a full kismesis and that they don't get to kill each other.
So as well as the **** ton of characters in Homestuck, they are all sorted into these quadrants, and can exist in more than one even with the same character.