If Nick is a red herring my money is actually on Jacob. I feel like Rusty, Jamie, Leon, John-Boy, Derek and ofc the MC himself are automatically excluded. It's either Nick, Jacob or Tommy. Tommy could be squeezed for cash/his bad habbits, but he seems too direct for it. He serves his vengeance hot, not cold.
Nick is the prime suspect since the trashing, and his general sus attitude and close ties with Vinny, but it's also too obvious. Jacob asks a lot of questions, seems like a riot, but he also comes off as very calculated to me.