Despite his distaste for his first name, Cross is actually very well-named: Jeremiah was a prophet, and Cross knows what will happen to the Straw Hats if the events proceed without any interference.
Even better is the fact the Biblical Jeremiah failed to prevent a war, and Cross's greatest fear is failing to prevent the Marineford War.
In Chapter 20, Luffy is unaffected by B.R.O.B increasing the gravity, and even as it's warning him not to try anything foolish as it's much more powerful than him, Luffy flat out orders the entity to leave his friends alone. If you think about it a little more, Luffy is a D, and D's are the sworn enemies of the gods, especially jerkass ones.
Cross has another function on the crew: he's the lightning rod, and it's not only because he tanked the brunt of Eneru's wrath. A lightning rod diverts the electrical charge by taking it on himself to protect the house to suffer damage, just as Cross serves as a Butt-Monkey by enduring misfortune which should have fallen on his crewmates.
Vivi's Sovereign's Will was foreshadowed long before Enies Lobby: she managed to make Smoker and Eneru listen and obey to her. One could argue that Smoker doesn't count since he only bowed down when she revealed how prestigious her bloodline was, but Eneru has no such excuse.
Moria Awakening his Devil Fruit makes sense if one remembers his backstory. His first pirate crew was utterly decimated by Kaido and left him broken (mentally and physically). He then chose to create an immortal pirate crew made of the undead, along with his trump card of Oars, to take the Yonko on again. Moria would have been well on his way to get his revenge if it weren't for the Straw Hats showing up and annihilating his zombie crew. The mere thought of having a second crew annihilated while he was sedated and unable to do a thing about it was possibly a sufficiently traumatizing event to trigger the Awakening.
Perona's choice of the crow's nest for her room stems from her past at Thriller Bark when she didn't trust the rest of the Mysterious Four with its location whenever she leaves her prone body behind. It's the most isolated location on the ship, hard to get into and heavily protected (at least from ground-based assaults rather than aerial) by the crew and Sunny's defenses.
Word of God says that Cross was pulled into the One Piece World when his future knowledge only extended as far as Chapter 800, the tail end of the Dressrosa arc. Meaning that they're going to enter the Yonko Saga, a battle against at least half of the four strongest pirates on the Grand Line, in a possibly altered timeline (for better or worse), more or less blind. Keep in mind the Nightmare Fuel that we've seen so far of Big Mom and Kaido. Eep...
Nami's reaction when Cross reveals how frail he is at the Twin Capes: when she hits Luffy or Zoro, they treat it as a small annoyance. Cross can't. And she went for the hit, and laid him unconscious for several minutes because she thought he could take it. What if she had hit harder? You can hear the question in her mind when she realizes she could have accidentally killed one of her crewmates.
During the Rainbow Mist special, Cross reunites with one of his friends from the real world. His friend reveals he'd been sent to JoJo's Bizarre Adventure by a BROB of his own. Cross's situation of being thrown into a fictional universe by a sadistic, god-like entity is scary, but the idea that there's more of them doing the same thing makes it horrifying.
What's worse, Cross' friend has apparently been in JoJo since Part 3! For context, Cross is 19, his friend is about in his 40s-50s, and when he first appears in the special, he's hunting down Pucci!
Ever wonder why Buggy the Clown, a guy who sailed the Grand Line with Gol D. Roger, would wind up fleeing into the safety of East Blue — widely acknowledged as "The Weakest Sea" — and hiding there instead of going after One Piece himself? Well, in this version of the setting, he saw his whole first crew eaten alive by Lily Carnation. In all likelihood, he was scared out of the Grand Line entirely by the trauma; despite his claims of claiming One Piece when they first met, Buggy probably never intended to go back near the New World again if he could help it.
Which raises another thought: could Buggy's weakness be a result of his skills naturally declining through a lack of a challenge combined with sheer trauma at what he went through on Omatsuri Island? Sort of an inversion of Took a Level in Badass? And with Lily Carnation now dead... could the catharsis give Buggy a chance to heal from his trauma, and maybe start getting back in the game for real?