One Piece: Grand Line 3 Point 5/WMG

Usopp will have some level of precognition.
The latent ability provides a bonus to his sharpshooting skills, as well as gives him some insight into future events. However, it's balanced out by two flaws: Cassandra Truth and a tendency to see worst-case scenarios, making him naturally paranoid.

His tall tales serve two purposes: in-universe, it's a method of coping with and relaying his visions in a way that doesn't get automatically rejected by others. On a meta level, meanwhile, it's a way of challenging the GM, who has to eventually translate his stories into the campaign in some fashion.

At least one of the players will be the opposite gender of their character.
Chopper seems like a good bet, but Franky or Brook would be far funnier. Plus, the latter would provide an easy way to crack jokes about the "Mary Sue becoms the Straw Hat's Musician" trend prior to his joining.

Usopp's player will eventually want to stop because they're not having fun.
Considering Luke lives by the Rule of Fun, this would come as a major gut punch to him... much like the actual arc.

Rika will eventually become Nico Robin's player
At least if the purple speech bubbles are any indication.

Before playing Robin, Rika will play Vivi.
And her decision to switch to Nico Robin will echo Cory's shunting his character template onto Roronoa Zoro. In her case, however, it will be based more on roleplaying, feeling that it'd be more in-character for Vivi to choose to stay in her kingdom, and wanting a more properly empowered character.

Franky's future player will play Vivi.
Hey, the color-coding would match...

Luke's All-Ones "Diplomacy Die" has a single 20 on it.
To account for those rare occasions when Luffy actually says the right thing.