Calliope explains the abilities of Princes and Bards here and discusses Rogues and Thieves abilities here. The other classes are left to speculation but some fans have come up with a pretty cool mass Classpect post. A class determines how the player will use their aspect so each combination of class and aspect can have a wide range of powers. 

I’m not sure if the godtiers will age completely. My guess is that they’ll age until they’re adults and then stay that way, eternally youthful. 

After learning that their session was null, Rose no longer wanted to play by the rules or play to win. In this new session Rose may be motivated to complete her quest since it looks like she will need the grist hoards of her planet to help Skaia give the Genesis Frog nutrients.

Yes, it was because the game hadn’t begun yet.

That Lil Cal was the one Gamzee had, in the green suit. 

It was most likely done with the alchemiter.

Serenity was last seen here with Roxy.

The details of the endgame situation in the game haven’t been discussed in-comic but my guess that the sprites may not be able to leave the Medium and enter the new universe with the players since they’re game constructs. I don’t want to say for sure though. 

The Felt are leprechauns and they display their romantic intentions by dancing and singing riddles which means that Clover wanted to be in a relationship with Caliborn. 

That would be Bec Noir.  He’s a tyrant with only one arm and one eye since. (Technically he has two eyes but one of them is cut so yeah)