What is black's plan?
A general guideline when you're not sure is to play for expansion where the pawn chains are "pointing". In this case, your pawn chain is pointing toward the queenside. Moves like Rb8 and Nd7 to help pressure the c3 knight and b2 pawn. That's where you're going to create targets in white's camp.
I have probably played this a million times as black and I'm sure I never play it right. It's too easy for white to block the b-file with Bb3 so I don't think Rb8 is necessarily the right way to go, although I could be wrong. Looking at it now, I am thinking. e5, Qe7, Be6 and some rook to d8 planning on d5. Black has the extra pawn in the center. I would try to use it.
e5 seems counterproductive when you consider it limits the scope of the dark bishop and creates a target on d6. After 1...e5 2.Qd3 Qe7 3.Rad1 Rd8 4.f4! White has a much better position now.
Try to move the mispositioned rook between King and Queen
Bb7!, putting pressure on e4 and aiming to White's castled king. Other moves to be considered in the future (the order would need deeper analysis): a5, Nd7
I woudn't do that while White's light-squared bishop is aiming at f7.
I'm not sure white is "much" better after this but I will concede that having to move the rook off of f8 is unpleasant. Given your line, I would suggest something else for black. Rb8 makes sense but I don't see how to get white to cough up some weaknesses. He just plays Bb3. Maybe Qa5 and Nd7.
Maybe ..c5 to make it a more sicilian setup. This does weaken your d5 and b5, but your a1 diagonal becomes stronger (+ you get b6). Then moves like Rb8 and Qb6 and Nd7 look good to me. Your main attacking would be on the queenside over the a1 diagonal and the b-line. Your a-pawn can push (maybe with the help of Bd7) to meddle with your opponents queenside structure.