Their purpose was to assist the players but also to repopulate their abandoned home planet. The later is shown with Alternia and Spades Slick

that’s what Mystery the seahorse said on the Spongebob cartoon animated television show that one time back in 2002 and Eridan’s dad is also an seahorse

I think’s anything and all things are possible in one timeline or another

It’s still in use. It just became less talked about. People were shown captachaloging stuff well into Act 6 but the narrative didn’t always explicitly say so.

Caliborn has something, and Latula takes meds for some disorder, and probably some 3rd or possibly even 4th character I’ve neglected to mention.

After! John comes back and has a short conversation with John before John leaves and Terezi gives him the scarf.

Well, we see an explosion and then Crabdad dead in the next page so yes but technically no

Exactly

Homestuck is a computer game. That was our cursor interacting with the story. You can see the MSPA reader at their computer a few times throughout the story. As well as the actual Homestuck disks and cartridge in late A5A2 and Mid-Act 6 respectively 

WV and PM seem to have a nice ending.